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Add a comment on is_trivially_sized about obviously !Sized types

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Anthony Ramine 2020-09-12 18:35:32 +02:00
parent 88197214b8
commit 4f0047ed10
1 changed files with 6 additions and 0 deletions
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6
compiler/rustc_middle/src/ty/sty.rs
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@ -2280,6 +2280,12 @@ impl<'tcx> TyS<'tcx> {
/// ///
/// Returning true means the type is known to be sized. Returning /// Returning true means the type is known to be sized. Returning
/// `false` means nothing -- could be sized, might not be. /// `false` means nothing -- could be sized, might not be.
///
/// Note that we could never rely on the fact that a type such as `[_]` is
/// trivially `!Sized` because we could be in a type environment with a
/// bound such as `[_]: Copy`. A function with such a bound obviously never
/// can be called, but that doesn't mean it shouldn't typecheck. This is why
/// this method doesn't return `Option<bool>`.
pub fn is_trivially_sized(&self, tcx: TyCtxt<'tcx>) -> bool { pub fn is_trivially_sized(&self, tcx: TyCtxt<'tcx>) -> bool {
match self.kind() { match self.kind() {
ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) ty::Infer(ty::IntVar(_) | ty::FloatVar(_))