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std/meta: make FieldEnum(T) == Tag(T) for tagged unions when values match field indices

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Silver 2022-09-20 14:40:43 +01:00 committed by Veikka Tuominen
parent c75e8f3616
commit f3a1b5c481
1 changed files with 23 additions and 0 deletions
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23
lib/std/meta.zig
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@ -606,6 +606,18 @@ test "std.meta.tags" {
pub fn FieldEnum(comptime T: type) type {
const field_infos = fields(T);
if (@typeInfo(T) == .Union) {
if (@typeInfo(T).Union.tag_type) |tag_type| {
for (std.enums.values(tag_type)) |v, i| {
if (@enumToInt(v) != i) break; // enum values not consecutive
if (!std.mem.eql(u8, @tagName(v), field_infos[i].name)) break; // fields out of order
} else {
return tag_type;
}
}
}
var enumFields: [field_infos.len]std.builtin.Type.EnumField = undefined;
var decls = [_]std.builtin.Type.Declaration{};
inline for (field_infos) |field, i| {
@ -669,6 +681,17 @@ test "std.meta.FieldEnum" {
try expectEqualEnum(enum { a }, FieldEnum(struct { a: u8 }));
try expectEqualEnum(enum { a, b, c }, FieldEnum(struct { a: u8, b: void, c: f32 }));
try expectEqualEnum(enum { a, b, c }, FieldEnum(union { a: u8, b: void, c: f32 }));
const Tagged = union(enum) { a: u8, b: void, c: f32 };
try testing.expectEqual(Tag(Tagged), FieldEnum(Tagged));
const Tag2 = enum { b, c, a };
const Tagged2 = union(Tag2) { a: u8, b: void, c: f32 };
try testing.expect(Tag(Tagged2) != FieldEnum(Tagged2));
const Tag3 = enum(u8) { a, b, c = 7 };
const Tagged3 = union(Tag3) { a: u8, b: void, c: f32 };
try testing.expect(Tag(Tagged3) != FieldEnum(Tagged3));
}
pub fn DeclEnum(comptime T: type) type {