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Rollup merge of rust-lang#66755 - mark-i-m:const-vec-new, r=ecstatic-…
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…morse

Remove a const-if-hack in RawVec

r? @ecstatic-morse

cc @Centril
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Centril authored Dec 20, 2019
2 parents 696735f + 7d26811 commit 57da9d3
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Showing 2 changed files with 4 additions and 18 deletions.
1 change: 1 addition & 0 deletions src/liballoc/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,7 @@
#![feature(const_generic_impls_guard)]
#![feature(const_generics)]
#![feature(const_in_array_repeat_expressions)]
#![feature(const_if_match)]
#![feature(cow_is_borrowed)]
#![feature(dispatch_from_dyn)]
#![feature(core_intrinsics)]
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21 changes: 3 additions & 18 deletions src/liballoc/raw_vec.rs
Original file line number Diff line number Diff line change
Expand Up @@ -52,15 +52,12 @@ impl<T, A: Alloc> RawVec<T, A> {
/// Like `new`, but parameterized over the choice of allocator for
/// the returned `RawVec`.
pub const fn new_in(a: A) -> Self {
// `!0` is `usize::MAX`. This branch should be stripped at compile time.
// FIXME(mark-i-m): use this line when `if`s are allowed in `const`:
//let cap = if mem::size_of::<T>() == 0 { !0 } else { 0 };
let cap = if mem::size_of::<T>() == 0 { core::usize::MAX } else { 0 };

// `Unique::empty()` doubles as "unallocated" and "zero-sized allocation".
RawVec {
ptr: Unique::empty(),
// FIXME(mark-i-m): use `cap` when ifs are allowed in const
cap: [0, !0][(mem::size_of::<T>() == 0) as usize],
cap,
a,
}
}
Expand Down Expand Up @@ -132,19 +129,7 @@ impl<T> RawVec<T, Global> {
/// `RawVec` with capacity `usize::MAX`. Useful for implementing
/// delayed allocation.
pub const fn new() -> Self {
// FIXME(Centril): Reintegrate this with `fn new_in` when we can.

// `!0` is `usize::MAX`. This branch should be stripped at compile time.
// FIXME(mark-i-m): use this line when `if`s are allowed in `const`:
//let cap = if mem::size_of::<T>() == 0 { !0 } else { 0 };

// `Unique::empty()` doubles as "unallocated" and "zero-sized allocation".
RawVec {
ptr: Unique::empty(),
// FIXME(mark-i-m): use `cap` when ifs are allowed in const
cap: [0, !0][(mem::size_of::<T>() == 0) as usize],
a: Global,
}
Self::new_in(Global)
}

/// Creates a `RawVec` (on the system heap) with exactly the
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