| ... | @@ -459,3 +459,77 @@ test "write empty array to end" { | ... | @@ -459,3 +459,77 @@ test "write empty array to end" { |
| 459 | array[5..5].* = [_]u8{}; | 459 | array[5..5].* = [_]u8{}; |
| 460 | try testing.expectEqualStrings("hello", &array); | 460 | try testing.expectEqualStrings("hello", &array); |
| 461 | } | 461 | } |
| | 462 | |
| | 463 | fn doublePtrTest() !void { |
| | 464 | var a: u32 = 0; |
| | 465 | const ptr = &a; |
| | 466 | const double_ptr = &ptr; |
| | 467 | setDoublePtr(double_ptr, 1); |
| | 468 | setDoublePtr(double_ptr, 2); |
| | 469 | setDoublePtr(double_ptr, 1); |
| | 470 | try std.testing.expect(a == 1); |
| | 471 | } |
| | 472 | fn setDoublePtr(ptr: *const *const u32, value: u32) void { |
| | 473 | setPtr(ptr.*, value); |
| | 474 | } |
| | 475 | fn setPtr(ptr: *const u32, value: u32) void { |
| | 476 | const mut_ptr: *u32 = @constCast(ptr); |
| | 477 | mut_ptr.* = value; |
| | 478 | } |
| | 479 | test "double pointer can mutate comptime state" { |
| | 480 | try comptime doublePtrTest(); |
| | 481 | } |
| | 482 | |
| | 483 | fn GenericIntApplier( |
| | 484 | comptime Context: type, |
| | 485 | comptime applyFn: fn (context: Context, arg: u32) void, |
| | 486 | ) type { |
| | 487 | return struct { |
| | 488 | context: Context, |
| | 489 | |
| | 490 | const Self = @This(); |
| | 491 | |
| | 492 | inline fn any(self: *const Self) IntApplier { |
| | 493 | return .{ |
| | 494 | .context = @ptrCast(&self.context), |
| | 495 | .applyFn = typeErasedApplyFn, |
| | 496 | }; |
| | 497 | } |
| | 498 | |
| | 499 | fn typeErasedApplyFn(context: *const anyopaque, arg: u32) void { |
| | 500 | const ptr: *const Context = @alignCast(@ptrCast(context)); |
| | 501 | applyFn(ptr.*, arg); |
| | 502 | } |
| | 503 | }; |
| | 504 | } |
| | 505 | const IntApplier = struct { |
| | 506 | context: *const anyopaque, |
| | 507 | applyFn: *const fn (context: *const anyopaque, arg: u32) void, |
| | 508 | |
| | 509 | fn apply(ia: IntApplier, arg: u32) void { |
| | 510 | ia.applyFn(ia.context, arg); |
| | 511 | } |
| | 512 | }; |
| | 513 | const Accumulator = struct { |
| | 514 | value: u32, |
| | 515 | |
| | 516 | const Applier = GenericIntApplier(*u32, add); |
| | 517 | |
| | 518 | fn applier(a: *Accumulator) Applier { |
| | 519 | return .{ .context = &a.value }; |
| | 520 | } |
| | 521 | |
| | 522 | fn add(context: *u32, arg: u32) void { |
| | 523 | context.* += arg; |
| | 524 | } |
| | 525 | }; |
| | 526 | fn fieldPtrTest() u32 { |
| | 527 | var a: Accumulator = .{ .value = 0 }; |
| | 528 | const applier = a.applier(); |
| | 529 | applier.any().apply(1); |
| | 530 | applier.any().apply(1); |
| | 531 | return a.value; |
| | 532 | } |
| | 533 | test "pointer in aggregate field can mutate comptime state" { |
| | 534 | try comptime std.testing.expect(fieldPtrTest() == 2); |
| | 535 | } |
Veikka Tuominen <git@vexu.eu> 2024-01-29 12:43:17+02:00
src