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doc(array,vec): add notes about side effects when empty-initializing #79918

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4 changes: 4 additions & 0 deletions library/alloc/src/macros.rs
Original file line number Diff line number Diff line change
@@ -29,6 +29,10 @@
/// to the same boxed integer value, not five references pointing to independently
/// boxed integers.
///
/// Also, note that `vec![expr; 0]` is allowed, and produces an empty vector.
/// This will still evaluate `expr`, however, and immediately drop the resulting value, so
/// be mindful of side effects.
///
/// [`Vec`]: crate::vec::Vec
#[cfg(not(test))]
#[macro_export]
4 changes: 4 additions & 0 deletions library/std/src/primitive_docs.rs
Original file line number Diff line number Diff line change
@@ -489,6 +489,10 @@ mod prim_pointer {}
/// * A repeat expression `[x; N]`, which produces an array with `N` copies of `x`.
/// The type of `x` must be [`Copy`].
///
/// Note that `[expr; 0]` is allowed, and produces an empty array.
/// This will still evaluate `expr`, however, and immediately drop the resulting value, so
/// be mindful of side effects.
///
/// Arrays of *any* size implement the following traits if the element type allows it:
///
/// - [`Copy`]