mathieu/os-rust
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

'borrowed pointer' -> 'reference'

Browse source
This commit is contained in:
Brian Anderson 2014-01-07 18:49:13 -08:00
parent b65b4d6384
commit d323632669
39 changed files with 185 additions and 186 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

12
doc/complement-lang-faq.md
View file

@ -218,13 +218,13 @@ They start small (ideally in the hundreds of bytes) and expand dynamically by ca
* Managed boxes may not be shared between tasks
* Owned boxes may be transferred (moved) between tasks
## What is the difference between a borrowed pointer (`&`) and managed and owned boxes?
## What is the difference between a reference (`&`) and managed and owned boxes?
* Borrowed pointers point to the interior of a stack _or_ heap allocation
* Borrowed pointers can only be formed when it will provably be outlived by the referent
* Borrowed pointers to managed box pointers keep the managed boxes alive
* Borrowed pointers to owned boxes prevent their ownership from being transferred
* Borrowed pointers employ region-based alias analysis to ensure correctness
* References point to the interior of a stack _or_ heap allocation
* References can only be formed when it will provably be outlived by the referent
* References to managed box pointers keep the managed boxes alive
* References to owned boxes prevent their ownership from being transferred
* References employ region-based alias analysis to ensure correctness
## Why aren't function signatures inferred? Why only local slots?

2
doc/guide-ffi.md
View file

@ -417,7 +417,7 @@ However, there are currently no guarantees about the layout of an `enum`.
Rust's owned and managed boxes use non-nullable pointers as handles which point to the contained
object. However, they should not be manually created because they are managed by internal
allocators. Borrowed pointers can safely be assumed to be non-nullable pointers directly to the
allocators. References can safely be assumed to be non-nullable pointers directly to the
type. However, breaking the borrow checking or mutability rules is not guaranteed to be safe, so
prefer using raw pointers (`*`) if that's needed because the compiler can't make as many assumptions
about them.

72
doc/guide-lifetimes.md
View file

@ -1,22 +1,22 @@
% The Rust Borrowed Pointers and Lifetimes Guide
% The Rust References and Lifetimes Guide
# Introduction
Borrowed pointers are one of the more flexible and powerful tools available in
Rust. A borrowed pointer can point anywhere: into the managed or exchange
References are one of the more flexible and powerful tools available in
Rust. A reference can point anywhere: into the managed or exchange
heap, into the stack, and even into the interior of another data structure. A
borrowed pointer is as flexible as a C pointer or C++ reference. However,
reference is as flexible as a C pointer or C++ reference. However,
unlike C and C++ compilers, the Rust compiler includes special static checks
that ensure that programs use borrowed pointers safely. Another advantage of
borrowed pointers is that they are invisible to the garbage collector, so
working with borrowed pointers helps reduce the overhead of automatic memory
that ensure that programs use references safely. Another advantage of
references is that they are invisible to the garbage collector, so
working with references helps reduce the overhead of automatic memory
management.
Despite their complete safety, a borrowed pointer's representation at runtime
Despite their complete safety, a reference's representation at runtime
is the same as that of an ordinary pointer in a C program. They introduce zero
overhead. The compiler does all safety checks at compile time.
Although borrowed pointers have rather elaborate theoretical
Although references have rather elaborate theoretical
underpinnings (region pointers), the core concepts will be familiar to
anyone who has worked with C or C++. Therefore, the best way to explain
how they are used—and their limitations—is probably just to work
@ -24,8 +24,8 @@ through several examples.
# By example
Borrowed pointers are called *borrowed* because they are only valid for
a limited duration. Borrowed pointers never claim any kind of ownership
References, sometimes known as *borrowed pointers*, are only valid for
a limited duration. References never claim any kind of ownership
over the data that they point to: instead, they are used for cases
where you would like to use data for a short time.
@ -55,7 +55,7 @@ define it this way, calling the function will cause the points to be
copied. For points, this is probably not so bad, but often copies are
expensive. Worse, if the data type contains mutable fields, copying can change
the semantics of your program in unexpected ways. So we'd like to define a
function that takes the points by pointer. We can use borrowed pointers to do
function that takes the points by pointer. We can use references to do
this:
~~~
@ -89,7 +89,7 @@ name for the same data.
In contrast, we can pass the boxes `managed_box` and `owned_box` to
`compute_distance` directly. The compiler automatically converts a box like
`@Point` or `~Point` to a borrowed pointer like `&Point`. This is another form
`@Point` or `~Point` to a reference like `&Point`. This is another form
of borrowing: in this case, the caller lends the contents of the managed or
owned box to the callee.
@ -100,7 +100,7 @@ addition, the compiler will reject any code that might cause the borrowed
value to be freed or overwrite its component fields with values of different
types (I'll get into what kinds of actions those are shortly). This rule
should make intuitive sense: you must wait for a borrower to return the value
that you lent it (that is, wait for the borrowed pointer to go out of scope)
that you lent it (that is, wait for the reference to go out of scope)
before you can make full use of it again.
# Other uses for the & operator
@ -114,7 +114,7 @@ let on_the_stack: Point = Point {x: 3.0, y: 4.0};
This declaration means that code can only pass `Point` by value to other
functions. As a consequence, we had to explicitly take the address of
`on_the_stack` to get a borrowed pointer. Sometimes however it is more
`on_the_stack` to get a reference. Sometimes however it is more
convenient to move the & operator into the definition of `on_the_stack`:
~~~
@ -180,7 +180,7 @@ as well as from the managed box, and then compute the distance between them.
We’ve seen a few examples so far of borrowing heap boxes, both managed
and owned. Up till this point, we’ve glossed over issues of
safety. As stated in the introduction, at runtime a borrowed pointer
safety. As stated in the introduction, at runtime a reference
is simply a pointer, nothing more. Therefore, avoiding C's problems
with dangling pointers requires a compile-time safety check.
@ -195,7 +195,7 @@ broader scope than the pointer itself), the compiler reports an
error. We'll be discussing lifetimes more in the examples to come, and
a more thorough introduction is also available.
When the `&` operator creates a borrowed pointer, the compiler must
When the `&` operator creates a reference, the compiler must
ensure that the pointer remains valid for its entire
lifetime. Sometimes this is relatively easy, such as when taking the
address of a local variable or a field that is stored on the stack:
@ -209,7 +209,7 @@ fn example1() {
} // -+
~~~
Here, the lifetime of the borrowed pointer `y` is simply L, the
Here, the lifetime of the reference `y` is simply L, the
remainder of the function body. The compiler need not do any other
work to prove that code will not free `x.f`. This is true even if the
code mutates `x`.
@ -384,7 +384,7 @@ enum Shape {
~~~
Now we might write a function to compute the area of a shape. This
function takes a borrowed pointer to a shape, to avoid the need for
function takes a reference to a shape, to avoid the need for
copying.
~~~
@ -466,19 +466,19 @@ same rules as the ones we saw for borrowing the interior of a owned
box: it must be able to guarantee that the `enum` will not be
overwritten for the duration of the borrow. In fact, the compiler
would accept the example we gave earlier. The example is safe because
the shape pointer has type `&Shape`, which means "borrowed pointer to
the shape pointer has type `&Shape`, which means "reference to
immutable memory containing a `shape`". If, however, the type of that
pointer were `&mut Shape`, then the ref binding would be ill-typed.
Just as with owned boxes, the compiler will permit `ref` bindings
into data owned by the stack frame even if the data are mutable,
but otherwise it requires that the data reside in immutable memory.
# Returning borrowed pointers
# Returning references
So far, all of the examples we have looked at, use borrowed pointers in a
So far, all of the examples we have looked at, use references in a
“downward” direction. That is, a method or code block creates a
borrowed pointer, then uses it within the same scope. It is also
possible to return borrowed pointers as the result of a function, but
reference, then uses it within the same scope. It is also
possible to return references as the result of a function, but
as we'll see, doing so requires some explicit annotation.
For example, we could write a subroutine like this:
@ -496,7 +496,7 @@ explicitly. So in effect, this function declares that it takes a
pointer with lifetime `r` and returns a pointer with that same
lifetime.
In general, it is only possible to return borrowed pointers if they
In general, it is only possible to return references if they
are derived from a parameter to the procedure. In that case, the
pointer result will always have the same lifetime as one of the
parameters; named lifetimes indicate which parameter that
@ -532,10 +532,10 @@ fn get_x_sh(p: @Point) -> &f64 {
~~~
Here, the function `get_x_sh()` takes a managed box as input and
returns a borrowed pointer. As before, the lifetime of the borrowed
pointer that will be returned is a parameter (specified by the
caller). That means that `get_x_sh()` promises to return a borrowed
pointer that is valid for as long as the caller would like: this is
returns a reference. As before, the lifetime of the reference
that will be returned is a parameter (specified by the
caller). That means that `get_x_sh()` promises to return a reference
that is valid for as long as the caller would like: this is
subtly different from the first example, which promised to return a
pointer that was valid for as long as its pointer argument was valid.
@ -551,10 +551,10 @@ valid at all once it returns, as the parameter `p` may or may not be
live in the caller. Therefore, the compiler will report an error here.
In general, if you borrow a managed (or owned) box to create a
borrowed pointer, the pointer will only be valid within the function
and cannot be returned. This is why the typical way to return borrowed
pointers is to take borrowed pointers as input (the only other case in
which it can be legal to return a borrowed pointer is if the pointer
reference, it will only be valid within the function
and cannot be returned. This is why the typical way to return references
is to take references as input (the only other case in
which it can be legal to return a reference is if it
points at a static constant).
# Named lifetimes
@ -577,7 +577,7 @@ fn select<'r, T>(shape: &'r Shape, threshold: f64,
}
~~~
This function takes three borrowed pointers and assigns each the same
This function takes three references and assigns each the same
lifetime `r`. In practice, this means that, in the caller, the
lifetime `r` will be the *intersection of the lifetime of the three
region parameters*. This may be overly conservative, as in this
@ -657,7 +657,7 @@ This is equivalent to the previous definition.
# Conclusion
So there you have it: a (relatively) brief tour of the borrowed pointer
So there you have it: a (relatively) brief tour of the lifetime
system. For more details, we refer to the (yet to be written) reference
document on borrowed pointers, which will explain the full notation
document on references, which will explain the full notation
and give more examples.

18
doc/guide-pointers.md
View file

@ -86,8 +86,8 @@ common, such as C++, please read "A note..." below.
or impossible. This is only often useful when a program is very large or very
complicated. Using a managed pointer will activate Rust's garbage collection
mechanism.
5: Borrowed: You're writing a function, and you need a pointer, but you don't
care about its ownership. If you make the argument a borrowed pointer, callers
5: Reference: You're writing a function, and you need a pointer, but you don't
care about its ownership. If you make the argument a reference, callers
can send in whatever kind they want.
Five exceptions. That's it. Otherwise, you shouldn't need them. Be skeptical
@ -313,11 +313,11 @@ drawback.
concurrency boundaries is the source of endless pain in other langauges, so
Rust does not let you do this.
# Borrowed Pointers
# References
Borrowed pointers are the third major kind of pointer Rust supports. They are
References are the third major kind of pointer Rust supports. They are
simultaneously the simplest and the most complicated kind. Let me explain:
they're called 'borrowed' pointers because they claim no ownership over the
references are considered 'borrowed' because they claim no ownership over the
data they're pointing to. They're just borrowing it for a while. So in that
sense, they're simple: just keep whatever ownership the data already has. For
example:
@ -346,13 +346,13 @@ fn main() {
~~~
This prints `5.83095189`. You can see that the `compute_distance` function
takes in two borrowed pointers, but we give it a managed and unique pointer. Of
takes in two references, but we give it a managed and unique pointer. Of
course, if this were a real program, we wouldn't have any of these pointers,
they're just there to demonstrate the concepts.
So how is this hard? Well, because we're igorning ownership, the compiler needs
to take great care to make sure that everything is safe. Despite their complete
safety, a borrowed pointer's representation at runtime is the same as that of
safety, a reference's representation at runtime is the same as that of
an ordinary pointer in a C program. They introduce zero overhead. The compiler
does all safety checks at compile time.
@ -416,8 +416,8 @@ test.rs:4 let y = &x;
~~~
As you might guess, this kind of analysis is complex for a human, and therefore
hard for a computer, too! There is an entire [tutorial devoted to borrowed
pointers and lifetimes](tutorial-lifetimes.html) that goes into lifetimes in
hard for a computer, too! There is an entire [guide devoted to references
and lifetimes](guide-lifetimes.html) that goes into lifetimes in
great detail, so if you want the full details, check that out.
# Returning Pointers

2
doc/index.md
View file

@ -12,7 +12,7 @@
# Guides
[Pointers](guide-pointers.html)
[Lifetimes](guide-lifetimes.html)
[References and Lifetimes](guide-lifetimes.html)
[Containers and Iterators](guide-container.html)
[Tasks and Communication](guide-tasks.html)
[Foreign Function Interface](guide-ffi.html)

42
doc/rust.md
View file

@ -1215,7 +1215,7 @@ A static item must have a _constant expression_ giving its definition.
Static items must be explicitly typed.
The type may be ```bool```, ```char```, a number, or a type derived from those primitive types.
The derived types are borrowed pointers with the `'static` lifetime,
The derived types are references with the `'static` lifetime,
fixed-size arrays, tuples, and structs.
~~~~
@ -1841,7 +1841,7 @@ A complete list of the built-in language items follows:
`owned`
: Are uniquely owned.
`durable`
: Contain borrowed pointers.
: Contain references.
`drop`
: Have finalizers.
`add`
@ -1898,11 +1898,11 @@ A complete list of the built-in language items follows:
`free`
: Free memory that was allocated on the managed heap.
`borrow_as_imm`
: Create an immutable borrowed pointer to a mutable value.
: Create an immutable reference to a mutable value.
`return_to_mut`
: Release a borrowed pointer created with `return_to_mut`
: Release a reference created with `return_to_mut`
`check_not_borrowed`
: Fail if a value has existing borrowed pointers to it.
: Fail if a value has existing references to it.
`strdup_uniq`
: Return a new unique string
containing a copy of the contents of a unique string.
@ -2199,7 +2199,7 @@ When an lvalue is evaluated in an _lvalue context_, it denotes a memory location
when evaluated in an _rvalue context_, it denotes the value held _in_ that memory location.
When an rvalue is used in lvalue context, a temporary un-named lvalue is created and used instead.
A temporary's lifetime equals the largest lifetime of any borrowed pointer that points to it.
A temporary's lifetime equals the largest lifetime of any reference that points to it.
#### Moved and copied types
@ -2403,8 +2403,8 @@ before the expression they apply to.
: [Boxing](#pointer-types) operators. Allocate a box to hold the value they are applied to,
and store the value in it. `@` creates a managed box, whereas `~` creates an owned box.
`&`
: Borrow operator. Returns a borrowed pointer, pointing to its operand.
The operand of a borrowed pointer is statically proven to outlive the resulting pointer.
: Borrow operator. Returns a reference, pointing to its operand.
The operand of a borrow is statically proven to outlive the resulting pointer.
If the borrow-checker cannot prove this, it is a compilation error.
### Binary operator expressions
@ -2894,9 +2894,9 @@ match x {
Patterns that bind variables
default to binding to a copy or move of the matched value
(depending on the matched value's type).
This can be changed to bind to a borrowed pointer by
This can be changed to bind to a reference by
using the ```ref``` keyword,
or to a mutable borrowed pointer using ```ref mut```.
or to a mutable reference using ```ref mut```.
A pattern that's just an identifier,
like `Nil` in the previous answer,
@ -3172,18 +3172,18 @@ Owning pointers (`~`)
it involves allocating a new owned box and copying the contents of the old box into the new box.
Releasing an owning pointer immediately releases its corresponding owned box.
Borrowed pointers (`&`)
References (`&`)
: These point to memory _owned by some other value_.
Borrowed pointers arise by (automatic) conversion from owning pointers, managed pointers,
References arise by (automatic) conversion from owning pointers, managed pointers,
or by applying the borrowing operator `&` to some other value,
including [lvalues, rvalues or temporaries](#lvalues-rvalues-and-temporaries).
Borrowed pointers are written `&content`, or in some cases `&'f content` for some lifetime-variable `f`,
for example `&int` means a borrowed pointer to an integer.
Copying a borrowed pointer is a "shallow" operation:
References are written `&content`, or in some cases `&'f content` for some lifetime-variable `f`,
for example `&int` means a reference to an integer.
Copying a reference is a "shallow" operation:
it involves only copying the pointer itself.
Releasing a borrowed pointer typically has no effect on the value it points to,
Releasing a reference typically has no effect on the value it points to,
with the exception of temporary values,
which are released when the last borrowed pointer to them is released.
which are released when the last reference to them is released.
Raw pointers (`*`)
: Raw pointers are pointers without safety or liveness guarantees.
@ -3338,7 +3338,7 @@ The kinds are:
This kind includes scalars and immutable references,
as well as structural types containing other `Pod` types.
`'static`
: Types of this kind do not contain any borrowed pointers;
: Types of this kind do not contain any references;
this can be a useful guarantee for code
that breaks borrowing assumptions
using [`unsafe` operations](#unsafe-functions).
@ -3417,14 +3417,14 @@ frame they are allocated within.
### Memory ownership
A task owns all memory it can *safely* reach through local variables,
as well as managed, owning and borrowed pointers.
as well as managed, owned boxes and references.
When a task sends a value that has the `Send` trait to another task,
it loses ownership of the value sent and can no longer refer to it.
This is statically guaranteed by the combined use of "move semantics",
and the compiler-checked _meaning_ of the `Send` trait:
it is only instantiated for (transitively) sendable kinds of data constructor and pointers,
never including managed or borrowed pointers.
never including managed boxes or references.
When a stack frame is exited, its local allocations are all released, and its
references to boxes (both managed and owned) are dropped.
@ -3569,7 +3569,7 @@ These include:
- simple locks and semaphores
When such facilities carry values, the values are restricted to the [`Send` type-kind](#type-kinds).
Restricting communication interfaces to this kind ensures that no borrowed or managed pointers move between tasks.
Restricting communication interfaces to this kind ensures that no references or managed pointers move between tasks.
Thus access to an entire data structure can be mediated through its owning "root" value;
no further locking or copying is required to avoid data races within the substructure of such a value.

48
doc/tutorial.md
View file

@ -1341,11 +1341,12 @@ let mut y = ~5; // mutable
*y += 2; // the * operator is needed to access the contained value
~~~~
# Borrowed pointers
# References
Rust's borrowed pointers are a general purpose reference type. In contrast with
In contrast with
owned boxes, where the holder of an owned box is the owner of the pointed-to
memory, borrowed pointers never imply ownership. A pointer can be borrowed to
memory, references never imply ownership - they are "borrowed".
A reference can be borrowed to
any object, and the compiler verifies that it cannot outlive the lifetime of
the object.
@ -1377,7 +1378,7 @@ to define a function that takes two arguments of type point—that is,
it takes the points by value. But this will cause the points to be
copied when we call the function. For points, this is probably not so
bad, but often copies are expensive. So we’d like to define a function
that takes the points by pointer. We can use borrowed pointers to do this:
that takes the points by pointer. We can use references to do this:
~~~
# struct Point { x: f64, y: f64 }
@ -1410,7 +1411,7 @@ route to the same data.
In the case of the boxes `managed_box` and `owned_box`, however, no
explicit action is necessary. The compiler will automatically convert
a box like `@point` or `~point` to a borrowed pointer like
a box like `@point` or `~point` to a reference like
`&point`. This is another form of borrowing; in this case, the
contents of the managed/owned box are being lent out.
@ -1420,11 +1421,11 @@ have been lent out, you cannot send that variable to another task, nor
will you be permitted to take actions that might cause the borrowed
value to be freed or to change its type. This rule should make
intuitive sense: you must wait for a borrowed value to be returned
(that is, for the borrowed pointer to go out of scope) before you can
(that is, for the reference to go out of scope) before you can
make full use of it again.
For a more in-depth explanation of borrowed pointers and lifetimes, read the
[lifetimes and borrowed pointer tutorial][lifetimes].
For a more in-depth explanation of references and lifetimes, read the
[references and lifetimes guide][lifetimes].
## Freezing
@ -1622,8 +1623,7 @@ defined in [`std::vec`] and [`std::str`].
# Ownership escape hatches
Ownership can cleanly describe tree-like data structures, and borrowed pointers provide non-owning
references. However, more flexibility is often desired and Rust provides ways to escape from strict
Ownership can cleanly describe tree-like data structures, and refercences provide non-owning pointers. However, more flexibility is often desired and Rust provides ways to escape from strict
single parent ownership.
The standard library provides the `std::rc::Rc` pointer type to express *shared ownership* over a
@ -1880,7 +1880,7 @@ A caller must in turn have a compatible pointer type to call the method.
# Rectangle(Point, Point)
# }
impl Shape {
fn draw_borrowed(&self) { ... }
fn draw_reference(&self) { ... }
fn draw_managed(@self) { ... }
fn draw_owned(~self) { ... }
fn draw_value(self) { ... }
@ -1890,13 +1890,13 @@ let s = Circle(Point { x: 1.0, y: 2.0 }, 3.0);
(@s).draw_managed();
(~s).draw_owned();
(&s).draw_borrowed();
(&s).draw_reference();
s.draw_value();
~~~
Methods typically take a borrowed pointer self type,
Methods typically take a reference self type,
so the compiler will go to great lengths to convert a callee
to a borrowed pointer.
to a reference.
~~~
# fn draw_circle(p: Point, f: f64) { }
@ -1907,27 +1907,27 @@ to a borrowed pointer.
# Rectangle(Point, Point)
# }
# impl Shape {
# fn draw_borrowed(&self) { ... }
# fn draw_reference(&self) { ... }
# fn draw_managed(@self) { ... }
# fn draw_owned(~self) { ... }
# fn draw_value(self) { ... }
# }
# let s = Circle(Point { x: 1.0, y: 2.0 }, 3.0);
// As with typical function arguments, managed and owned pointers
// are automatically converted to borrowed pointers
// are automatically converted to references
(@s).draw_borrowed();
(~s).draw_borrowed();
(@s).draw_reference();
(~s).draw_reference();
// Unlike typical function arguments, the self value will
// automatically be referenced ...
s.draw_borrowed();
s.draw_reference();
// ... and dereferenced
(& &s).draw_borrowed();
(& &s).draw_reference();
// ... and dereferenced and borrowed
(&@~s).draw_borrowed();
(&@~s).draw_reference();
~~~
Implementations may also define standalone (sometimes called "static")
@ -2095,7 +2095,7 @@ and may not be overridden:
* `Send` - Sendable types.
Types are sendable
unless they contain managed boxes, managed closures, or borrowed pointers.
unless they contain managed boxes, managed closures, or references.
* `Freeze` - Constant (immutable) types.
These are types that do not contain anything intrinsically mutable.
@ -2104,7 +2104,7 @@ Intrinsically mutable values include `Cell` in the standard library.
* `'static` - Non-borrowed types.
These are types that do not contain any data whose lifetime is bound to
a particular stack frame. These are types that do not contain any
borrowed pointers, or types where the only contained borrowed pointers
references, or types where the only contained references
have the `'static` lifetime.
> ***Note:*** These two traits were referred to as 'kinds' in earlier
@ -2439,7 +2439,7 @@ order to be packaged up in a trait object of that storage class.
* The contents of owned traits (`~Trait`) must fulfill the `Send` bound.
* The contents of managed traits (`@Trait`) must fulfill the `'static` bound.
* The contents of borrowed traits (`&Trait`) are not constrained by any bound.
* The contents of reference traits (`&Trait`) are not constrained by any bound.
Consequently, the trait objects themselves automatically fulfill their
respective kind bounds. However, this default behavior can be overridden by

4
src/libextra/future.rs
View file

@ -60,8 +60,8 @@ impl<A> Future<A> {
pub fn get_ref<'a>(&'a mut self) -> &'a A {
/*!
* Executes the future's closure and then returns a borrowed
* pointer to the result. The borrowed pointer lasts as long as
* Executes the future's closure and then returns a reference
* to the result. The reference lasts as long as
* the future.
*/
match self.state {

2
src/libextra/sync.rs
View file

@ -431,7 +431,7 @@ struct RWLockInner {
// (or reader/downgrader) race.
// By the way, if we didn't care about the assert in the read unlock path,
// we could instead store the mode flag in write_downgrade's stack frame,
// and have the downgrade tokens store a borrowed pointer to it.
// and have the downgrade tokens store a reference to it.
read_mode: bool,
// The only way the count flag is ever accessed is with xadd. Since it is
// a read-modify-write operation, multiple xadds on different cores will

22
src/librustc/middle/borrowck/doc.rs
View file

@ -44,7 +44,7 @@ referent).
It then uses the dataflow module to propagate which of those borrows
may be in scope at each point in the procedure. A loan is considered
to come into scope at the expression that caused it and to go out of
scope when the lifetime of the resulting borrowed pointer expires.
scope when the lifetime of the resulting reference expires.
Once the in-scope loans are known for each point in the program, the
borrow checker walks the IR again in a second pass called
@ -146,14 +146,14 @@ result of the borrow `&mut (*x).f` in the example above:
The loan states that the expression `(*x).f` has been loaned as
mutable for the lifetime `'a`. Because the loan is mutable, that means
that the value `(*x).f` may be mutated via the newly created borrowed
pointer (and *only* via that pointer). This is reflected in the
that the value `(*x).f` may be mutated via the newly created reference
(and *only* via that pointer). This is reflected in the
restrictions `RS` that accompany the loan.
The first restriction `((*x).f, [MUTATE, CLAIM, FREEZE])` states that
the lender may not mutate nor freeze `(*x).f`. Mutation is illegal
because `(*x).f` is only supposed to be mutated via the new borrowed
pointer, not by mutating the original path `(*x).f`. Freezing is
because `(*x).f` is only supposed to be mutated via the new reference,
not by mutating the original path `(*x).f`. Freezing is
illegal because the path now has an `&mut` alias; so even if we the
lender were to consider `(*x).f` to be immutable, it might be mutated
via this alias. Both of these restrictions are temporary. They will be
@ -164,8 +164,8 @@ The second restriction on `*x` is interesting because it does not
apply to the path that was lent (`(*x).f`) but rather to a prefix of
the borrowed path. This is due to the rules of inherited mutability:
if the user were to assign to (or freeze) `*x`, they would indirectly
overwrite (or freeze) `(*x).f`, and thus invalidate the borrowed
pointer that was created. In general it holds that when a path is
overwrite (or freeze) `(*x).f`, and thus invalidate the reference
that was created. In general it holds that when a path is
lent, restrictions are issued for all the owning prefixes of that
path. In this case, the path `*x` owns the path `(*x).f` and,
because `x` is an owned pointer, the path `x` owns the path `*x`.
@ -241,7 +241,7 @@ lvalue `LV` being borrowed and the mutability `MQ` and lifetime `LT`
of the resulting pointer. Given those, `gather_loans` applies three
validity tests:
1. `MUTABILITY(LV, MQ)`: The mutability of the borrowed pointer is
1. `MUTABILITY(LV, MQ)`: The mutability of the reference is
compatible with the mutability of `LV` (i.e., not borrowing immutable
data as mutable).
@ -380,9 +380,9 @@ of its owner:
TYPE(LV) = ~Ty
LIFETIME(LV, LT, MQ)
### Checking lifetime for derefs of borrowed pointers
### Checking lifetime for derefs of references
Borrowed pointers have a lifetime `LT'` associated with them. The
References have a lifetime `LT'` associated with them. The
data they point at has been guaranteed to be valid for at least this
lifetime. Therefore, the borrow is valid so long as the lifetime `LT`
of the borrow is shorter than the lifetime `LT'` of the pointer
@ -412,7 +412,7 @@ value is not mutated or moved. Note that lvalues are either
(ultimately) owned by a local variable, in which case we can check
whether that local variable is ever moved in its scope, or they are
owned by the referent of an (immutable, due to condition 2) managed or
borrowed pointer, in which case moves are not permitted because the
references, in which case moves are not permitted because the
location is aliasable.
If the conditions of `L-Deref-Managed-Imm-User-Root` are not met, then

2
src/librustc/middle/borrowck/gather_loans/mod.rs
View file

@ -662,7 +662,7 @@ impl<'a> GatherLoanCtxt<'a> {
//! &mut v.counter
//! }
//!
//! In this case, the borrowed pointer (`'a`) outlives the
//! In this case, the reference (`'a`) outlives the
//! variable `v` that hosts it. Note that this doesn't come up
//! with immutable `&` pointers, because borrows of such pointers
//! do not require restrictions and hence do not cause a loan.

2
src/librustc/middle/borrowck/mod.rs
View file

@ -719,7 +719,7 @@ impl BorrowckCtxt {
err_out_of_scope(super_scope, sub_scope) => {
note_and_explain_region(
self.tcx,
"borrowed pointer must be valid for ",
"reference must be valid for ",
sub_scope,
"...");
note_and_explain_region(

2
src/librustc/middle/check_const.rs
View file

@ -192,7 +192,7 @@ pub fn check_expr(v: &mut CheckCrateVisitor,
ExprAddrOf(..) => {
sess.span_err(
e.span,
"borrowed pointers in constants may only refer to \
"references in constants may only refer to \
immutable values");
},
ExprVstore(_, ExprVstoreUniq) |

23
src/librustc/middle/kind.rs
View file

@ -33,7 +33,7 @@ use syntax::visit::Visitor;
// send: Things that can be sent on channels or included in spawned closures.
// freeze: Things thare are deeply immutable. They are guaranteed never to
// change, and can be safely shared without copying between tasks.
// 'static: Things that do not contain borrowed pointers.
// 'static: Things that do not contain references.
//
// Send includes scalar types as well as classes and unique types containing
// only sendable types.
@ -487,12 +487,11 @@ pub fn check_durable(tcx: ty::ctxt, ty: ty::t, sp: Span) -> bool {
if !ty::type_is_static(tcx, ty) {
match ty::get(ty).sty {
ty::ty_param(..) => {
tcx.sess.span_err(sp, "value may contain borrowed \
pointers; add `'static` bound");
tcx.sess.span_err(sp, "value may contain references; \
add `'static` bound");
}
_ => {
tcx.sess.span_err(sp, "value may contain borrowed \
pointers");
tcx.sess.span_err(sp, "value may contain references");
}
}
false
@ -502,10 +501,10 @@ pub fn check_durable(tcx: ty::ctxt, ty: ty::t, sp: Span) -> bool {
}
/// This is rather subtle. When we are casting a value to a instantiated
/// trait like `a as trait<'r>`, regionck already ensures that any borrowed
/// pointers that appear in the type of `a` are bounded by `'r` (ed.: rem
/// trait like `a as trait<'r>`, regionck already ensures that any references
/// that appear in the type of `a` are bounded by `'r` (ed.: rem
/// FIXME(#5723)). However, it is possible that there are *type parameters*
/// in the type of `a`, and those *type parameters* may have borrowed pointers
/// in the type of `a`, and those *type parameters* may have references
/// within them. We have to guarantee that the regions which appear in those
/// type parameters are not obscured.
///
@ -513,17 +512,17 @@ pub fn check_durable(tcx: ty::ctxt, ty: ty::t, sp: Span) -> bool {
///
/// (1) The trait instance cannot escape the current fn. This is
/// guaranteed if the region bound `&r` is some scope within the fn
/// itself. This case is safe because whatever borrowed pointers are
/// itself. This case is safe because whatever references are
/// found within the type parameter, they must enclose the fn body
/// itself.
///
/// (2) The type parameter appears in the type of the trait. For
/// example, if the type parameter is `T` and the trait type is
/// `deque<T>`, then whatever borrowed ptrs may appear in `T` also
/// `deque<T>`, then whatever references may appear in `T` also
/// appear in `deque<T>`.
///
/// (3) The type parameter is sendable (and therefore does not contain
/// borrowed ptrs).
/// references).
///
/// FIXME(#5723)---This code should probably move into regionck.
pub fn check_cast_for_escaping_regions(
@ -573,7 +572,7 @@ pub fn check_cast_for_escaping_regions(
// if !target_regions.iter().any(|t_r| is_subregion_of(cx, *t_r, r)) {
// cx.tcx.sess.span_err(
// source_span,
// format!("source contains borrowed pointer with lifetime \
// format!("source contains reference with lifetime \
// not found in the target type `{}`",
// ty_to_str(cx.tcx, target_ty)));
// note_and_explain_region(

2
src/librustc/middle/moves.rs
View file

@ -612,7 +612,7 @@ impl VisitContext {
self.use_receiver(receiver_expr);
// for overloaded operatrs, we are always passing in a
// borrowed pointer, so it's always read mode:
// reference, so it's always read mode:
for arg_expr in arg_exprs.iter() {
self.use_expr(*arg_expr, Read);
}

4
src/librustc/middle/ty.rs
View file

@ -1752,7 +1752,7 @@ fn type_needs_unwind_cleanup_(cx: ctxt, ty: t,
* think of them as kind of an "anti-kind". They track the kinds of values
* and thinks that are contained in types. Having a larger contents for
* a type tends to rule that type *out* from various kinds. For example,
* a type that contains a borrowed pointer is not sendable.
* a type that contains a reference is not sendable.
*
* The reason we compute type contents and not kinds is that it is
* easier for me (nmatsakis) to think about what is contained within
@ -2188,7 +2188,7 @@ pub fn type_contents(cx: ctxt, ty: t) -> TypeContents {
mutbl: ast::Mutability)
-> TypeContents {
/*!
* Type contents due to containing a borrowed pointer
* Type contents due to containing a reference
* with the region `region` and borrow kind `bk`
*/

22
src/librustc/middle/typeck/check/regionck.rs
View file

@ -789,10 +789,10 @@ fn constrain_regions_in_type(
pub mod guarantor {
/*!
* The routines in this module are aiming to deal with the case
* where a the contents of a borrowed pointer are re-borrowed.
* Imagine you have a borrowed pointer `b` with lifetime L1 and
* where a the contents of a reference are re-borrowed.
* Imagine you have a reference `b` with lifetime L1 and
* you have an expression `&*b`. The result of this borrow will
* be another borrowed pointer with lifetime L2 (which is an
* be another reference with lifetime L2 (which is an
* inference variable). The borrow checker is going to enforce
* the constraint that L2 < L1, because otherwise you are
* re-borrowing data for a lifetime larger than the original loan.
@ -815,15 +815,15 @@ pub mod guarantor {
* a borrow.
*
* The key point here is that when you are borrowing a value that
* is "guaranteed" by a borrowed pointer, you must link the
* lifetime of that borrowed pointer (L1, here) to the lifetime of
* is "guaranteed" by a reference, you must link the
* lifetime of that reference (L1, here) to the lifetime of
* the borrow itself (L2). What do I mean by "guaranteed" by a
* borrowed pointer? I mean any data that is reached by first
* dereferencing a borrowed pointer and then either traversing
* reference? I mean any data that is reached by first
* dereferencing a reference and then either traversing
* interior offsets or owned pointers. We say that the guarantor
* of such data it the region of the borrowed pointer that was
* of such data it the region of the reference that was
* traversed. This is essentially the same as the ownership
* relation, except that a borrowed pointer never owns its
* relation, except that a reference never owns its
* contents.
*
* NB: I really wanted to use the `mem_categorization` code here
@ -953,7 +953,7 @@ pub mod guarantor {
guarantor: Option<ty::Region>) {
/*!
*
* Links the lifetime of the borrowed pointer resulting from a borrow
* Links the lifetime of the reference resulting from a borrow
* to the lifetime of its guarantor (if any).
*/
@ -1134,7 +1134,7 @@ pub mod guarantor {
Some(ty::AutoBorrowFn(r)) |
Some(ty::AutoBorrowObj(r, _)) => {
// If there is an autoref, then the result of this
// expression will be some sort of borrowed pointer.
// expression will be some sort of reference.
expr_ct.cat.guarantor = None;
expr_ct.cat.pointer = BorrowedPointer(r);
debug!("autoref, cat={:?}", expr_ct.cat);

2
src/librustc/middle/typeck/check/regionmanip.rs
View file

@ -146,7 +146,7 @@ pub fn relate_free_regions(
* for each function just before we check the body of that
* function, looking for types where you have a borrowed
* pointer to other borrowed data (e.g., `&'a &'b [uint]`.
* We do not allow borrowed pointers to outlive the things they
* We do not allow references to outlive the things they
* point at, so we can assume that `'a <= 'b`.
*
* Tests: `src/test/compile-fail/regions-free-region-ordering-*.rs`

6
src/librustc/middle/typeck/infer/coercion.rs
View file

@ -20,8 +20,8 @@ but not in representation (so actual subtyping is inappropriate).
## Reborrowing
Note that if we are expecting a borrowed pointer, we will *reborrow*
even if the argument provided was already a borrowed pointer. This is
Note that if we are expecting a reference, we will *reborrow*
even if the argument provided was already a reference. This is
useful for freezing mut/const things (that is, when the expected is &T
but you have &const T or &mut T) and also for avoiding the linearity
of mut things (when the expected is &mut T and you have &mut T). See
@ -451,7 +451,7 @@ impl Coerce {
let a_unsafe = ty::mk_ptr(self.get_ref().infcx.tcx, mt_a);
if_ok!(self.subtype(a_unsafe, b));
// although borrowed ptrs and unsafe ptrs have the same
// although references and unsafe ptrs have the same
// representation, we still register an AutoDerefRef so that
// regionck knows that the region for `a` must be valid here
Ok(Some(@AutoDerefRef(AutoDerefRef {

14
src/librustc/middle/typeck/infer/error_reporting.rs
View file

@ -226,11 +226,11 @@ impl ErrorReporting for InferCtxt {
infer::Reborrow(span) => {
self.tcx.sess.span_err(
span,
"lifetime of borrowed pointer outlines \
"lifetime of reference outlines \
lifetime of borrowed content...");
note_and_explain_region(
self.tcx,
"...the borrowed pointer is valid for ",
"...the reference is valid for ",
sub,
"...");
note_and_explain_region(
@ -351,7 +351,7 @@ impl ErrorReporting for InferCtxt {
infer::AddrOf(span) => {
self.tcx.sess.span_err(
span,
"borrowed pointer is not valid \
"reference is not valid \
at the time of borrow");
note_and_explain_region(
self.tcx,
@ -362,7 +362,7 @@ impl ErrorReporting for InferCtxt {
infer::AutoBorrow(span) => {
self.tcx.sess.span_err(
span,
"automatically borrowed pointer is not valid \
"automatically reference is not valid \
at the time of borrow");
note_and_explain_region(
self.tcx,
@ -532,7 +532,7 @@ impl ErrorReportingHelpers for InferCtxt {
infer::Reborrow(span) => {
self.tcx.sess.span_note(
span,
"...so that borrowed pointer does not outlive \
"...so that reference does not outlive \
borrowed content");
}
infer::InfStackClosure(span) => {
@ -586,13 +586,13 @@ impl ErrorReportingHelpers for InferCtxt {
infer::AddrOf(span) => {
self.tcx.sess.span_note(
span,
"...so that borrowed pointer is valid \
"...so that reference is valid \
at the time of borrow");
}
infer::AutoBorrow(span) => {
self.tcx.sess.span_note(
span,
"...so that automatically borrowed pointer is valid \
"...so that automatically reference is valid \
at the time of borrow");
}
infer::BindingTypeIsNotValidAtDecl(span) => {

4
src/librustc/middle/typeck/infer/mod.rs
View file

@ -157,7 +157,7 @@ pub enum SubregionOrigin {
// Invocation of closure must be within its lifetime
InvokeClosure(Span),
// Dereference of borrowed pointer must be within its lifetime
// Dereference of reference must be within its lifetime
DerefPointer(Span),
// Closure bound must not outlive captured free variables
@ -170,7 +170,7 @@ pub enum SubregionOrigin {
// relating `'a` to `'b`
RelateObjectBound(Span),
// Creating a pointer `b` to contents of another borrowed pointer
// Creating a pointer `b` to contents of another reference
Reborrow(Span),
// (&'a &'b T) where a >= b

8
src/librustc/middle/typeck/infer/region_inference/doc.rs
View file

@ -226,12 +226,12 @@ corresponds to the *actual execution of the function `add()`*, after
all arguments have been evaluated. There is a corresponding lifetime
`'b_call` for the execution of `inc()`. If we wanted to be precise
about it, the lifetime of the two borrows should be `'a_call` and
`'b_call` respectively, since the borrowed pointers that were created
`'b_call` respectively, since the references that were created
will not be dereferenced except during the execution itself.
However, this model by itself is not sound. The reason is that
while the two borrowed pointers that are created will never be used
simultaneously, it is still true that the first borrowed pointer is
while the two references that are created will never be used
simultaneously, it is still true that the first reference is
*created* before the second argument is evaluated, and so even though
it will not be *dereferenced* during the evaluation of the second
argument, it can still be *invalidated* by that evaluation. Consider
@ -257,7 +257,7 @@ invalidating the first argument.
So, for now, we exclude the `call` lifetimes from our model.
Eventually I would like to include them, but we will have to make the
borrow checker handle this situation correctly. In particular, if
there is a borrowed pointer created whose lifetime does not enclose
there is a reference created whose lifetime does not enclose
the borrow expression, we must issue sufficient restrictions to ensure
that the pointee remains valid.

2
src/librustc/middle/typeck/rscope.rs
View file

@ -19,7 +19,7 @@ use syntax::opt_vec::OptVec;
/// Defines strategies for handling regions that are omitted. For
/// example, if one writes the type `&Foo`, then the lifetime of of
/// this borrowed pointer has been omitted. When converting this
/// this reference has been omitted. When converting this
/// type, the generic functions in astconv will invoke `anon_regions`
/// on the provided region-scope to decide how to translate this
/// omitted region.

2
src/libstd/borrow.rs
View file

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Borrowed pointer utilities
//! Utilities for references
#[cfg(not(test))]
use prelude::*;

4
src/libstd/cast.rs
View file

@ -64,7 +64,7 @@ pub unsafe fn transmute<L, G>(thing: L) -> G {
#[inline]
pub unsafe fn transmute_mut<'a,T>(ptr: &'a T) -> &'a mut T { transmute(ptr) }
/// Coerce a borrowed pointer to have an arbitrary associated region.
/// Coerce a reference to have an arbitrary associated region.
#[inline]
pub unsafe fn transmute_region<'a,'b,T>(ptr: &'a T) -> &'b T {
transmute(ptr)
@ -82,7 +82,7 @@ pub unsafe fn transmute_immut_unsafe<T,P:RawPtr<T>>(ptr: P) -> *T {
transmute(ptr)
}
/// Coerce a borrowed mutable pointer to have an arbitrary associated region.
/// Coerce a mutable reference to have an arbitrary associated region.
#[inline]
pub unsafe fn transmute_mut_region<'a,'b,T>(ptr: &'a mut T) -> &'b mut T {
transmute(ptr)

2
src/libstd/clone.rs
View file

@ -59,7 +59,7 @@ impl<T> Clone for @T {
}
impl<'a, T> Clone for &'a T {
/// Return a shallow copy of the borrowed pointer.
/// Return a shallow copy of the reference.
#[inline]
fn clone(&self) -> &'a T { *self }
}

2
src/libstd/lib.rs
View file

@ -18,7 +18,7 @@
//! `std` includes modules corresponding to each of the integer types,
//! each of the floating point types, the `bool` type, tuples, characters,
//! strings (`str`), vectors (`vec`), managed boxes (`managed`), owned
//! boxes (`owned`), and unsafe and borrowed pointers (`ptr`, `borrowed`).
//! boxes (`owned`), and unsafe pointers and references (`ptr`, `borrowed`).
//! Additionally, `std` provides pervasive types (`option` and `result`),
//! task creation and communication primitives (`task`, `comm`), platform
//! abstractions (`os` and `path`), basic I/O abstractions (`io`), common

2
src/libstd/vec.rs
View file

@ -71,7 +71,7 @@ traits from other modules. Some notable examples:
## Iteration
The method `iter()` returns an iteration value for a vector or a vector slice.
The iterator yields borrowed pointers to the vector's elements, so if the element
The iterator yields references to the vector's elements, so if the element
type of the vector is `int`, the element type of the iterator is `&int`.
```rust

2
src/libsyntax/ast.rs
View file

@ -371,7 +371,7 @@ pub enum Pat_ {
PatTup(~[@Pat]),
PatBox(@Pat),
PatUniq(@Pat),
PatRegion(@Pat), // borrowed pointer pattern
PatRegion(@Pat), // reference pattern
PatLit(@Expr),
PatRange(@Expr, @Expr),
// [a, b, ..i, y, z] is represented as

2
src/libsyntax/ext/deriving/generic.rs
View file

@ -26,7 +26,7 @@ Supported features (fairly exhaustive):
requires an explicit `Eq` bound at the
moment. (`TraitDef.additional_bounds`)
Unsupported: FIXME #6257: calling methods on borrowed pointer fields,
Unsupported: FIXME #6257: calling methods on reference fields,
e.g. deriving TotalEq/TotalOrd/Clone don't work on `struct A(&int)`,
because of how the auto-dereferencing happens.

2
src/libsyntax/util/interner.rs
View file

@ -83,7 +83,7 @@ impl<T:Eq + IterBytes + Hash + Freeze + Clone + 'static> Interner<T> {
}
// A StrInterner differs from Interner<String> in that it accepts
// borrowed pointers rather than @ ones, resulting in less allocation.
// references rather than @ ones, resulting in less allocation.
pub struct StrInterner {
priv map: @RefCell<HashMap<@str, Name>>,
priv vect: @RefCell<~[@str]>,

2
src/test/compile-fail/box-static-bound.rs
View file

@ -1,7 +1,7 @@
#[feature(managed_boxes)];
fn f<T>(x: T) -> @T {
@x //~ ERROR value may contain borrowed pointers
@x //~ ERROR value may contain references
}
fn g<T:'static>(x: T) -> @T {

2
src/test/compile-fail/core-tls-store-pointer.rs
View file

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// Testing that we can't store a borrowed pointer it task-local storage
// Testing that we can't store a reference it task-local storage
use std::local_data;

10
src/test/compile-fail/kindck-owned-trait-scoped.rs
View file

@ -23,8 +23,8 @@ impl<T:Clone> foo for T {
}
fn to_foo<T:Clone>(t: T) {
// This version is ok because, although T may contain borrowed
// pointers, it never escapes the fn body. We know this because
// This version is ok because, although T may contain references
// it never escapes the fn body. We know this because
// the type of foo includes a region which will be resolved to
// the fn body itself.
let v = &3;
@ -34,15 +34,15 @@ fn to_foo<T:Clone>(t: T) {
}
fn to_foo_2<T:Clone>(t: T) -> @foo {
// Not OK---T may contain borrowed ptrs and it is going to escape
// Not OK---T may contain references and it is going to escape
// as part of the returned foo value
struct F<T> { f: T }
@F {f:t} as @foo //~ ERROR value may contain borrowed pointers; add `'static` bound
@F {f:t} as @foo //~ ERROR value may contain references; add `'static` bound
}
fn to_foo_3<T:Clone + 'static>(t: T) -> @foo {
// OK---T may escape as part of the returned foo value, but it is
// owned and hence does not contain borrowed ptrs
// owned and hence does not contain references
struct F<T> { f: T }
@F {f:t} as @foo
}

4
src/test/compile-fail/kindck-owned-trait.rs
View file

@ -14,9 +14,9 @@ trait foo { fn foo(&self); }
fn to_foo<T:Clone + foo>(t: T) -> @foo {
@t as @foo
//~^ ERROR value may contain borrowed pointers; add `'static` bound
//~^ ERROR value may contain references; add `'static` bound
//~^^ ERROR cannot pack type
//~^^^ ERROR value may contain borrowed pointers
//~^^^ ERROR value may contain references
}
fn to_foo2<T:Clone + foo + 'static>(t: T) -> @foo {

4
src/test/compile-fail/regions-trait-2.rs
View file

@ -10,7 +10,7 @@
// xfail-test #5723
// Test that you cannot escape a borrowed pointer
// Test that you cannot escape a reference
// into a trait.
struct ctxt { v: uint }
@ -29,7 +29,7 @@ fn make_gc() -> @get_ctxt {
let ctxt = ctxt { v: 22u };
let hc = has_ctxt { c: &ctxt };
return @hc as @get_ctxt;
//^~ ERROR source contains borrowed pointer
//^~ ERROR source contains reference
}
fn main() {

4
src/test/debug-info/destructured-local.rs
View file

@ -175,10 +175,10 @@ fn main() {
// managed box
let @aa = @(34, 35);
// borrowed pointer
// reference
let &bb = &(36, 37);
// contained borrowed pointer
// contained reference
let (&cc, _) = (&38, 39);
// unique pointer

2
src/test/run-pass/issue-3563-3.rs
View file

@ -51,7 +51,7 @@ struct AsciiArt {
priv lines: ~[~[char]],
// This struct can be quite large so we'll disable copying: developers need
// to either pass these structs around via borrowed pointers or move them.
// to either pass these structs around via references or move them.
}
impl Drop for AsciiArt {

8
src/test/run-pass/issue-5708.rs
View file

@ -9,12 +9,12 @@
// except according to those terms.
/*
# ICE when returning struct with borrowed pointer to trait
# ICE when returning struct with reference to trait
A function which takes a borrowed pointer to a trait and returns a
struct with that borrowed pointer results in an ICE.
A function which takes a reference to a trait and returns a
struct with that reference results in an ICE.
This does not occur with concrete types, only with borrowed pointers
This does not occur with concrete types, only with references
to traits.
*/