Date: Tue, 2 Aug 2022 01:32:35 +0000
From: Gregory Anders <greg@gpanders.com>
To: Peter Bridge <peter_bridge@hotmail.com>
Cc: ~andrewrk/ziglang@lists.sr.ht
Subject: Re: std.mem.eql and sentinels
Message-ID: <Yuh+sxH3pZRY3wlZ@gpanders.com>
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On Mon, 01 Aug 2022 15:55 +0200, Peter Bridge wrote:
>Are these considered equal?
>
>const a = [_:0]u8{ '4', '2'};
>const b = [_]u8{ '4', '2'};
>
>I am not sure how I could even check the sentinels match, or if it 
>even matters :) but since I still have some custom string utils (some 
>with sentinels, and some without (wasm not C)), I want to also have 
>some tests to make sure they are adding/not adding sentinels in the 
>correct place.  But then I get index of of bounds...  Any tips on how 
>to test such functions please? Cheers Peter

"Equal" in what sense? They have different types, but they would compare
equal element-wise.

Sentinels are encoded in the type system. To check if a given variable
has a sentinel you can check the type info using @typeInfo, e.g.

     @typeInfo(@TypeOf(a)).Array.sentinel

There are also some handy functions in std.meta for this kind of
thing, e.g. std.meta.sentinel:

     const std = @import("std");
     test {
         const a = [_:0]u8{ '4', '2' };
         const b = [_]u8{ '4', '2' };

         try std.testing.expectEqual(std.meta.sentinel(@TypeOf(a)), 0);
         try std.testing.expectEqual(std.meta.sentinel(@TypeOf(b)), null);
     }

Greg