Update Box::from_raw example to generalize better #73678
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I know very little about rust, so I saw this example and tried to generalize it by writing,
```
let layout = Layout::new::<T>();
let new_obj = unsafe {
let ptr = alloc(layout) as *mut T;
*ptr = obj;
Box::from_raw(ptr)
};
```
for some more complicated `T`, which ended up crashing with SIGSEGV,
because it tried to `drop_in_place` the previous object in `ptr` which is
of course garbage. I also added a comment that explains why `.write`
is used, but I think adding that comment is optional and may be too verbose
here. I do however think that changing this example is a good idea to
suggest the correct generalization. `.write` is also used in most of the rest
of the documentation here, even if the example is `i32`, so it would additionally
be more consistent.
|
Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @LukasKalbertodt (or someone else) soon. If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes. Please see the contribution instructions for more information. |
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Jun 28, 2020
|
@bors r+ rollup |
|
📌 Commit 0c88dd6 has been approved by |
bors
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Manishearth
added a commit
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Jun 29, 2020
Update Box::from_raw example to generalize better
I know very little about rust, so I saw the example here
```
use std::alloc::{alloc, Layout};
unsafe {
let ptr = alloc(Layout::new::<i32>()) as *mut i32;
*ptr = 5;
let x = Box::from_raw(ptr);
}
```
and tried to generalize it by writing,
```
let layout = Layout::new::<T>();
let new_obj = unsafe {
let ptr = alloc(layout) as *mut T;
*ptr = obj;
Box::from_raw(ptr)
};
```
for some more complicated `T`, which ended up crashing with SIGSEGV,
because it tried to `drop_in_place` the previous object in `ptr` which is
of course garbage. I think that changing this example to use `.write` instead
would be a good idea to suggest the correct generalization. It is also more
consistent with other documentation items in this file, which use `.write`.
I also added a comment to explain it, but I'm not too attached to that,
and can see it being too verbose in this place.
Manishearth
added a commit
to Manishearth/rust
that referenced
this pull request
Jun 29, 2020
Update Box::from_raw example to generalize better
I know very little about rust, so I saw the example here
```
use std::alloc::{alloc, Layout};
unsafe {
let ptr = alloc(Layout::new::<i32>()) as *mut i32;
*ptr = 5;
let x = Box::from_raw(ptr);
}
```
and tried to generalize it by writing,
```
let layout = Layout::new::<T>();
let new_obj = unsafe {
let ptr = alloc(layout) as *mut T;
*ptr = obj;
Box::from_raw(ptr)
};
```
for some more complicated `T`, which ended up crashing with SIGSEGV,
because it tried to `drop_in_place` the previous object in `ptr` which is
of course garbage. I think that changing this example to use `.write` instead
would be a good idea to suggest the correct generalization. It is also more
consistent with other documentation items in this file, which use `.write`.
I also added a comment to explain it, but I'm not too attached to that,
and can see it being too verbose in this place.
Manishearth
added a commit
to Manishearth/rust
that referenced
this pull request
Jun 30, 2020
Update Box::from_raw example to generalize better
I know very little about rust, so I saw the example here
```
use std::alloc::{alloc, Layout};
unsafe {
let ptr = alloc(Layout::new::<i32>()) as *mut i32;
*ptr = 5;
let x = Box::from_raw(ptr);
}
```
and tried to generalize it by writing,
```
let layout = Layout::new::<T>();
let new_obj = unsafe {
let ptr = alloc(layout) as *mut T;
*ptr = obj;
Box::from_raw(ptr)
};
```
for some more complicated `T`, which ended up crashing with SIGSEGV,
because it tried to `drop_in_place` the previous object in `ptr` which is
of course garbage. I think that changing this example to use `.write` instead
would be a good idea to suggest the correct generalization. It is also more
consistent with other documentation items in this file, which use `.write`.
I also added a comment to explain it, but I'm not too attached to that,
and can see it being too verbose in this place.
Manishearth
added a commit
to Manishearth/rust
that referenced
this pull request
Jun 30, 2020
Update Box::from_raw example to generalize better
I know very little about rust, so I saw the example here
```
use std::alloc::{alloc, Layout};
unsafe {
let ptr = alloc(Layout::new::<i32>()) as *mut i32;
*ptr = 5;
let x = Box::from_raw(ptr);
}
```
and tried to generalize it by writing,
```
let layout = Layout::new::<T>();
let new_obj = unsafe {
let ptr = alloc(layout) as *mut T;
*ptr = obj;
Box::from_raw(ptr)
};
```
for some more complicated `T`, which ended up crashing with SIGSEGV,
because it tried to `drop_in_place` the previous object in `ptr` which is
of course garbage. I think that changing this example to use `.write` instead
would be a good idea to suggest the correct generalization. It is also more
consistent with other documentation items in this file, which use `.write`.
I also added a comment to explain it, but I'm not too attached to that,
and can see it being too verbose in this place.
Manishearth
added a commit
to Manishearth/rust
that referenced
this pull request
Jun 30, 2020
Update Box::from_raw example to generalize better
I know very little about rust, so I saw the example here
```
use std::alloc::{alloc, Layout};
unsafe {
let ptr = alloc(Layout::new::<i32>()) as *mut i32;
*ptr = 5;
let x = Box::from_raw(ptr);
}
```
and tried to generalize it by writing,
```
let layout = Layout::new::<T>();
let new_obj = unsafe {
let ptr = alloc(layout) as *mut T;
*ptr = obj;
Box::from_raw(ptr)
};
```
for some more complicated `T`, which ended up crashing with SIGSEGV,
because it tried to `drop_in_place` the previous object in `ptr` which is
of course garbage. I think that changing this example to use `.write` instead
would be a good idea to suggest the correct generalization. It is also more
consistent with other documentation items in this file, which use `.write`.
I also added a comment to explain it, but I'm not too attached to that,
and can see it being too verbose in this place.
Manishearth
added a commit
to Manishearth/rust
that referenced
this pull request
Jul 1, 2020
Update Box::from_raw example to generalize better
I know very little about rust, so I saw the example here
```
use std::alloc::{alloc, Layout};
unsafe {
let ptr = alloc(Layout::new::<i32>()) as *mut i32;
*ptr = 5;
let x = Box::from_raw(ptr);
}
```
and tried to generalize it by writing,
```
let layout = Layout::new::<T>();
let new_obj = unsafe {
let ptr = alloc(layout) as *mut T;
*ptr = obj;
Box::from_raw(ptr)
};
```
for some more complicated `T`, which ended up crashing with SIGSEGV,
because it tried to `drop_in_place` the previous object in `ptr` which is
of course garbage. I think that changing this example to use `.write` instead
would be a good idea to suggest the correct generalization. It is also more
consistent with other documentation items in this file, which use `.write`.
I also added a comment to explain it, but I'm not too attached to that,
and can see it being too verbose in this place.
Manishearth
added a commit
to Manishearth/rust
that referenced
this pull request
Jul 1, 2020
Update Box::from_raw example to generalize better
I know very little about rust, so I saw the example here
```
use std::alloc::{alloc, Layout};
unsafe {
let ptr = alloc(Layout::new::<i32>()) as *mut i32;
*ptr = 5;
let x = Box::from_raw(ptr);
}
```
and tried to generalize it by writing,
```
let layout = Layout::new::<T>();
let new_obj = unsafe {
let ptr = alloc(layout) as *mut T;
*ptr = obj;
Box::from_raw(ptr)
};
```
for some more complicated `T`, which ended up crashing with SIGSEGV,
because it tried to `drop_in_place` the previous object in `ptr` which is
of course garbage. I think that changing this example to use `.write` instead
would be a good idea to suggest the correct generalization. It is also more
consistent with other documentation items in this file, which use `.write`.
I also added a comment to explain it, but I'm not too attached to that,
and can see it being too verbose in this place.
bors
added a commit
to rust-lang-ci/rust
that referenced
this pull request
Jul 1, 2020
…arth Rollup of 17 pull requests Successful merges: - rust-lang#72071 (Added detailed error code explanation for issue E0687 in Rust compiler.) - rust-lang#72369 (Bring net/parser.rs up to modern up to date with modern rust patterns) - rust-lang#72445 (Stabilize `#[track_caller]`.) - rust-lang#73466 (impl From<char> for String) - rust-lang#73548 (remove rustdoc warnings) - rust-lang#73649 (Fix sentence structure) - rust-lang#73678 (Update Box::from_raw example to generalize better) - rust-lang#73705 (stop taking references in Relate) - rust-lang#73716 (Document the static keyword) - rust-lang#73752 (Remap Windows ERROR_INVALID_PARAMETER to ErrorKind::InvalidInput from Other) - rust-lang#73776 (Move terminator to new module) - rust-lang#73778 (Make `likely` and `unlikely` const, gated by feature `const_unlikely`) - rust-lang#73805 (Document the type keyword) - rust-lang#73806 (Use an 'approximate' universal upper bound when reporting region errors) - rust-lang#73828 (Fix wording for anonymous parameter name help) - rust-lang#73846 (Fix comma in debug_assert! docs) - rust-lang#73847 (Edit cursor.prev() method docs in lexer) Failed merges: r? @ghost
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I know very little about rust, so I saw the example here
and tried to generalize it by writing,
for some more complicated
T, which ended up crashing with SIGSEGV,because it tried to
drop_in_placethe previous object inptrwhich isof course garbage. I think that changing this example to use
.writeinsteadwould be a good idea to suggest the correct generalization. It is also more
consistent with other documentation items in this file, which use
.write.I also added a comment to explain it, but I'm not too attached to that,
and can see it being too verbose in this place.