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Rollup merge of rust-lang#71095 - pickfire:box-from-array, r=dtolnay
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impl From<[T; N]> for Box<[T]>

Based on rust-lang#68692
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RalfJung authored May 29, 2020
2 parents 8120780 + a8ed9aa commit b387a11
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Showing 4 changed files with 44 additions and 6 deletions.
19 changes: 19 additions & 0 deletions src/liballoc/boxed.rs
Original file line number Diff line number Diff line change
Expand Up @@ -865,6 +865,25 @@ impl From<Box<str>> for Box<[u8]> {
}
}

#[stable(feature = "box_from_array", since = "1.45.0")]
impl<T, const N: usize> From<[T; N]> for Box<[T]>
where
[T; N]: LengthAtMost32,
{
/// Converts a `[T; N]` into a `Box<[T]>`
///
/// This conversion moves the array to newly heap-allocated memory.
///
/// # Examples
/// ```rust
/// let boxed: Box<[u8]> = Box::from([4, 2]);
/// println!("{:?}", boxed);
/// ```
fn from(array: [T; N]) -> Box<[T]> {
box array
}
}

#[stable(feature = "boxed_slice_try_from", since = "1.43.0")]
impl<T, const N: usize> TryFrom<Box<[T]>> for Box<[T; N]>
where
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,10 @@ pub fn yes_array_into_vec<T>() -> Vec<T> {
[].into()
}

pub fn yes_array_into_box<T>() -> Box<[T]> {
[].into()
}

use std::collections::VecDeque;

pub fn yes_vecdeque_partial_eq_array<A, B>() -> impl PartialEq<[B; 32]>
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,8 @@ pub fn no_box() {
let boxed_array = <Box<[i32; 33]>>::try_from(boxed_slice);
//~^ ERROR the trait bound `std::boxed::Box<[i32; 33]>: std::convert::From<std::boxed::Box<[i32]>>` is not satisfied
//~^^ ERROR the trait bound `std::boxed::Box<[i32; 33]>: std::convert::TryFrom<std::boxed::Box<[i32]>>` is not satisfied
let boxed_slice = <Box<[i32]>>::from([0; 33]);
//~^ 15:42: 15:49: arrays only have std trait implementations for lengths 0..=32 [E0277]
}

pub fn no_rc() {
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Original file line number Diff line number Diff line change
Expand Up @@ -18,10 +18,23 @@ LL | let boxed_array = <Box<[i32; 33]>>::try_from(boxed_slice);
<std::boxed::Box<(dyn std::error::Error + 'static)> as std::convert::From<&str>>
<std::boxed::Box<(dyn std::error::Error + 'static)> as std::convert::From<std::borrow::Cow<'a, str>>>
<std::boxed::Box<(dyn std::error::Error + 'static)> as std::convert::From<std::string::String>>
and 21 others
and 22 others
= note: required because of the requirements on the impl of `std::convert::Into<std::boxed::Box<[i32; 33]>>` for `std::boxed::Box<[i32]>`
= note: required because of the requirements on the impl of `std::convert::TryFrom<std::boxed::Box<[i32]>>` for `std::boxed::Box<[i32; 33]>`

error[E0277]: arrays only have std trait implementations for lengths 0..=32
--> $DIR/alloc-types-no-impls-length-33.rs:15:42
|
LL | let boxed_slice = <Box<[i32]>>::from([0; 33]);
| ^^^^^^^
| |
| expected an implementor of trait `std::convert::From<[{integer}; 33]>`
| help: consider borrowing here: `&[0; 33]`
|
= note: the trait bound `[i32; 33]: std::convert::From<[{integer}; 33]>` is not satisfied
= note: required because of the requirements on the impl of `std::convert::From<[i32; 33]>` for `std::boxed::Box<[i32]>`
= note: required by `std::convert::From::from`

error[E0277]: the trait bound `std::boxed::Box<[i32; 33]>: std::convert::TryFrom<std::boxed::Box<[i32]>>` is not satisfied
--> $DIR/alloc-types-no-impls-length-33.rs:12:23
|
Expand All @@ -32,7 +45,7 @@ LL | let boxed_array = <Box<[i32; 33]>>::try_from(boxed_slice);
<std::boxed::Box<[T; N]> as std::convert::TryFrom<std::boxed::Box<[T]>>>

error[E0277]: the trait bound `std::rc::Rc<[i32; 33]>: std::convert::From<std::rc::Rc<[i32]>>` is not satisfied
--> $DIR/alloc-types-no-impls-length-33.rs:19:23
--> $DIR/alloc-types-no-impls-length-33.rs:21:23
|
LL | let boxed_array = <Rc<[i32; 33]>>::try_from(boxed_slice);
| ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::convert::From<std::rc::Rc<[i32]>>` is not implemented for `std::rc::Rc<[i32; 33]>`
Expand All @@ -47,7 +60,7 @@ LL | let boxed_array = <Rc<[i32; 33]>>::try_from(boxed_slice);
= note: required because of the requirements on the impl of `std::convert::TryFrom<std::rc::Rc<[i32]>>` for `std::rc::Rc<[i32; 33]>`

error[E0277]: the trait bound `std::rc::Rc<[i32; 33]>: std::convert::TryFrom<std::rc::Rc<[i32]>>` is not satisfied
--> $DIR/alloc-types-no-impls-length-33.rs:19:23
--> $DIR/alloc-types-no-impls-length-33.rs:21:23
|
LL | let boxed_array = <Rc<[i32; 33]>>::try_from(boxed_slice);
| ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::convert::TryFrom<std::rc::Rc<[i32]>>` is not implemented for `std::rc::Rc<[i32; 33]>`
Expand All @@ -56,7 +69,7 @@ LL | let boxed_array = <Rc<[i32; 33]>>::try_from(boxed_slice);
<std::rc::Rc<[T; N]> as std::convert::TryFrom<std::rc::Rc<[T]>>>

error[E0277]: the trait bound `std::sync::Arc<[i32; 33]>: std::convert::From<std::sync::Arc<[i32]>>` is not satisfied
--> $DIR/alloc-types-no-impls-length-33.rs:26:23
--> $DIR/alloc-types-no-impls-length-33.rs:28:23
|
LL | let boxed_array = <Arc<[i32; 33]>>::try_from(boxed_slice);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::convert::From<std::sync::Arc<[i32]>>` is not implemented for `std::sync::Arc<[i32; 33]>`
Expand All @@ -71,14 +84,14 @@ LL | let boxed_array = <Arc<[i32; 33]>>::try_from(boxed_slice);
= note: required because of the requirements on the impl of `std::convert::TryFrom<std::sync::Arc<[i32]>>` for `std::sync::Arc<[i32; 33]>`

error[E0277]: the trait bound `std::sync::Arc<[i32; 33]>: std::convert::TryFrom<std::sync::Arc<[i32]>>` is not satisfied
--> $DIR/alloc-types-no-impls-length-33.rs:26:23
--> $DIR/alloc-types-no-impls-length-33.rs:28:23
|
LL | let boxed_array = <Arc<[i32; 33]>>::try_from(boxed_slice);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::convert::TryFrom<std::sync::Arc<[i32]>>` is not implemented for `std::sync::Arc<[i32; 33]>`
|
= help: the following implementations were found:
<std::sync::Arc<[T; N]> as std::convert::TryFrom<std::sync::Arc<[T]>>>

error: aborting due to 7 previous errors
error: aborting due to 8 previous errors

For more information about this error, try `rustc --explain E0277`.

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