46 lines
1.4 KiB
Zig
46 lines
1.4 KiB
Zig
const expect = @import("std").testing.expect;
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const print = @import("std").debug.print;
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// `opaque` types in Zig have an unknown (albeit non-zero) size and alignment.
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// Because of this these data types cannot be stored directly.
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// These are used to maintain type safety with pointers to types that we don't have information about.
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// ```zig
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// const Window = opaque {};
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// const Button = opaque {};
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// extern fn show_window(*Window) callconv(.C) void;
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// test "opaque" {
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// var main_window: *Window = undefined;
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// show_window(main_window);
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// var ok_button: *Button = undefined;
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// show_window(ok_button);
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// }
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//```
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// ./test-c1.zig:653:17: error: expected type '*Window', found '*Button'
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// show_window(ok_button);
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// ^
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// ./test-c1.zig:653:17: note: pointer type child 'Button' cannot cast into pointer type child 'Window'
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// show_window(ok_button);
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// ^
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// Opaque types may have declarations in their definitions (the same as structs, enums and unions).
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// XXX: This is a C function that is not defined in the Zig code.
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extern fn show_window(*Window) callconv(.C) void;
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const Window = opaque {
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fn show(self: *Window) void {
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show_window(self);
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}
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};
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test "opaque with declarations" {
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var main_window: *Window = undefined;
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main_window.show();
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}
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// The typical usecase of opaque is to maintain type safety
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// when interoperating with C code that does not expose complete type information.
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