From 173bc4274446a14aca2eea128b70b35b0ba18ebe Mon Sep 17 00:00:00 2001 From: Alex Kladov Date: Sat, 7 Jun 2025 18:07:53 +0100 Subject: [PATCH] langref: undefined _is_ materialized in all safe modes (#24107) * trailing whitespace * langref: undefined _is_ materialized in all safe modes I am also not super happy about the clause that immediately follows. I _believe_ what we want to say here is that, simultaneously: * undefined is guaranteed to be matrerialized in in all safe modes. A Zig implementation that elides `ptr.* = undefined` in ReleaseSafe mode would be a non-conforming implementation. * A Zig program that relies on undefined being materialized is buggy. But I don't think it's the time to engage this level of language-lawering! --- doc/langref.html.in | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/doc/langref.html.in b/doc/langref.html.in index 076b70e651..621cee3af5 100644 --- a/doc/langref.html.in +++ b/doc/langref.html.in @@ -777,7 +777,7 @@ value. Using this value would be a bug. The value will be unused, or overwritten before being used."

- In {#link|Debug#} mode, Zig writes {#syntax#}0xaa{#endsyntax#} bytes to undefined memory. This is to catch + In {#link|Debug#} and {#link|ReleaseSafe#} mode, Zig writes {#syntax#}0xaa{#endsyntax#} bytes to undefined memory. This is to catch bugs early, and to help detect use of undefined memory in a debugger. However, this behavior is only an implementation feature, not a language semantic, so it is not guaranteed to be observable to code.

@@ -2295,7 +2295,7 @@ or {#code|test_aligned_struct_fields.zig#}

- Equating packed structs results in a comparison of the backing integer, + Equating packed structs results in a comparison of the backing integer, and only works for the {#syntax#}=={#endsyntax#} and {#syntax#}!={#endsyntax#} {#link|Operators#}.

{#code|test_packed_struct_equality.zig#}