Type Function FieldEnum [src]

Returns an enum with a variant named after each field of T.

Prototype

pub fn FieldEnum(comptime T: type) type

Parameters

T: type

Example

 test FieldEnum {
    try expectEqualEnum(enum {}, FieldEnum(struct {}));
    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 { a, b, c };
    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));
}

Source

  pub fn FieldEnum(comptime T: type) type {
    const field_infos = fields(T);

    if (field_infos.len == 0) {
        return @Type(.{
            .@"enum" = .{
                .tag_type = u0,
                .fields = &.{},
                .decls = &.{},
                .is_exhaustive = true,
            },
        });
    }

    if (@typeInfo(T) == .@"union") {
        if (@typeInfo(T).@"union".tag_type) |tag_type| {
            for (std.enums.values(tag_type), 0..) |v, i| {
                if (@intFromEnum(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, 0..) |field, i| {
        enumFields[i] = .{
            .name = field.name ++ "",
            .value = i,
        };
    }
    return @Type(.{
        .@"enum" = .{
            .tag_type = std.math.IntFittingRange(0, field_infos.len - 1),
            .fields = &enumFields,
            .decls = &decls,
            .is_exhaustive = true,
        },
    });
}  