authorgravatar for sahnvour@pm.meSahnvour <sahnvour@pm.me> 2020-07-26 22:01:33+02:00
committergravatar for sahnvour@pm.meSahnvour <sahnvour@pm.me> 2020-07-26 22:01:33+02:00
log7ae1b3a6b348a24f07bacb6e19f1aa6d7b3ba32d
tree0659f3a27ae885a232e6dd975a4acd1639bb4f5e
parent3cdc0f104ee375a669d1a322da877df64255976b

add trait hasUniqueRepresentation

1 files changed, 68 insertions(+), 0 deletions(-)

lib/std/meta/trait.zig+68
...@@ -416,3 +416,71 @@ test "std.meta.trait.hasFunctions" {...@@ -416,3 +416,71 @@ test "std.meta.trait.hasFunctions" {
416 testing.expect(!hasFunctions(TestStruct2, .{ "a", "b", "c" }));416 testing.expect(!hasFunctions(TestStruct2, .{ "a", "b", "c" }));
417 testing.expect(!hasFunctions(TestStruct2, tuple));417 testing.expect(!hasFunctions(TestStruct2, tuple));
418}418}
419
420/// True if every value of the type `T` has a unique bit pattern representing it.
421/// In other words, `T` has no unused bits and no padding.
422pub fn hasUniqueRepresentation(comptime T: type) bool {
423 switch (@typeInfo(T)) {
424 else => return false, // TODO can we know if it's true for some of these types ?
425
426 .AnyFrame,
427 .Bool,
428 .BoundFn,
429 .Enum,
430 .ErrorSet,
431 .Fn,
432 .Int, // TODO check that it is still true
433 .Pointer,
434 => return true,
435
436 .Array => |info| return comptime hasUniqueRepresentation(info.child),
437
438 .Struct => |info| {
439 var sum_size = @as(usize, 0);
440
441 inline for (info.fields) |field| {
442 const FieldType = field.field_type;
443 if (comptime !hasUniqueRepresentation(FieldType)) return false;
444 sum_size += @sizeOf(FieldType);
445 }
446
447 return @sizeOf(T) == sum_size;
448 },
449
450 .Vector => |info| return comptime hasUniqueRepresentation(info.child),
451 }
452}
453
454test "std.meta.trait.hasUniqueRepresentation" {
455 const TestStruct1 = struct {
456 a: u32,
457 b: u32,
458 };
459
460 testing.expect(hasUniqueRepresentation(TestStruct1));
461
462 const TestStruct2 = struct {
463 a: u32,
464 b: u16,
465 };
466
467 testing.expect(!hasUniqueRepresentation(TestStruct2));
468
469 const TestStruct3 = struct {
470 a: u32,
471 b: u32,
472 };
473
474 testing.expect(hasUniqueRepresentation(TestStruct3));
475
476 testing.expect(hasUniqueRepresentation(i1));
477 testing.expect(hasUniqueRepresentation(u2));
478 testing.expect(hasUniqueRepresentation(i3));
479 testing.expect(hasUniqueRepresentation(u4));
480 testing.expect(hasUniqueRepresentation(i5));
481 testing.expect(hasUniqueRepresentation(u6));
482 testing.expect(hasUniqueRepresentation(i7));
483 testing.expect(hasUniqueRepresentation(u8));
484 testing.expect(hasUniqueRepresentation(i9));
485 testing.expect(hasUniqueRepresentation(u10));
486}