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std.mem.sliceTo: Return slice with sentinel from unbounded pointers

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Commit dec1163fbb removed sentinels from the returned slice for C
pointers. Since C pointers have no bounds, we know that it'll keep
scanning until it finds `end` (or crash trying). The same is also true
of many-item pointers without a sentinel (e.g. `[*]T`), so I added
support for those too.
This commit is contained in:
Jay Petacat 2025-12-05 11:43:28 -07:00
parent ea94ac52c5
commit 2ee4bd1072
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1 changed files with 13 additions and 2 deletions
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15
lib/std/mem.zig
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@ -913,8 +913,9 @@ fn SliceTo(comptime T: type, comptime end: std.meta.Elem(T)) type {
.pointer => |ptr_info| {
const Elem = std.meta.Elem(T);
const have_sentinel: bool = switch (ptr_info.size) {
.one, .slice, .many => if (std.meta.sentinel(T)) |s| s == end else false,
.c => false,
.one, .slice => if (std.meta.sentinel(T)) |s| s == end else false,
.many => if (std.meta.sentinel(T)) |s| s == end else true,
.c => true,
};
return @Pointer(.slice, .{
.@"const" = ptr_info.is_const,
@ -961,8 +962,15 @@ test sliceTo {
try testing.expectEqualSlices(u16, array[0..2], sliceTo(&array, 3));
try testing.expectEqualSlices(u16, array[0..2], sliceTo(array[0..3], 3));
const many_ptr: [*]u16 = &array;
try testing.expectEqualSlices(u16, array[0..2], sliceTo(many_ptr, 3));
try testing.expectEqual([:3]u16, @TypeOf(sliceTo(many_ptr, 3)));
const sentinel_ptr = @as([*:5]u16, @ptrCast(&array));
try testing.expectEqualSlices(u16, array[0..2], sliceTo(sentinel_ptr, 3));
try testing.expectEqual([]u16, @TypeOf(sliceTo(sentinel_ptr, 3)));
try testing.expectEqualSlices(u16, array[0..4], sliceTo(sentinel_ptr, 5));
try testing.expectEqual([:5]u16, @TypeOf(sliceTo(sentinel_ptr, 5)));
try testing.expectEqualSlices(u16, array[0..4], sliceTo(sentinel_ptr, 99));
const optional_sentinel_ptr = @as(?[*:5]u16, @ptrCast(&array));
@ -971,6 +979,7 @@ test sliceTo {
const c_ptr = @as([*c]u16, &array);
try testing.expectEqualSlices(u16, array[0..2], sliceTo(c_ptr, 3));
try testing.expectEqual([:3]u16, @TypeOf(sliceTo(c_ptr, 3)));
const slice: []u16 = &array;
try testing.expectEqualSlices(u16, array[0..2], sliceTo(slice, 3));
@ -1015,6 +1024,8 @@ fn lenSliceTo(ptr: anytype, comptime end: std.meta.Elem(@TypeOf(ptr))) usize {
var i: usize = 0;
while (ptr[i] != end and ptr[i] != s) i += 1;
return i;
} else {
return indexOfSentinel(ptr_info.child, end, @ptrCast(ptr));
},
.c => {
assert(ptr != null);