79 lines
2.4 KiB
Zig
79 lines
2.4 KiB
Zig
//
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// It'll only take us a moment to learn the Zig type coercion
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// rules because they're quite logical.
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//
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// 1. Types can always be made _more_ restrictive.
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//
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// var foo: u8 = 5;
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// var p1: *u8 = &foo;
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// var p2: *const u8 = p1; // mutable to immutable
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//
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// 2. Numeric types can coerce to _larger_ types.
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//
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// var n1: u8 = 5;
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// var n2: u16 = n1; // integer "widening"
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//
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// var n3: f16 = 42.0;
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// var n4: f32 = n3; // float "widening"
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//
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// 3. Single-item pointers to arrays coerce to slices and
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// many-item pointers.
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//
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// const arr: [3]u8 = [3]u8{5, 6, 7};
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// const s: []const u8 = &arr; // to slice
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// const p: [*]const u8 = &arr; // to many-item pointer
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//
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// 4. Single-item mutable pointers can coerce to single-item
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// pointers pointing to an array of length 1. (Interesting!)
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//
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// var five: u8 = 5;
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// var a_five: *[1]u8 = &five;
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//
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// 5. Payload types and null coerce to optionals.
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//
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// var num: u8 = 5;
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// var maybe_num: ?u8 = num; // payload type
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// maybe_num = null; // null
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//
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// 6. Payload types and errors coerce to error unions.
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//
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// const MyError = error{Argh};
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// var char: u8 = 'x';
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// var char_or_die: MyError!u8 = char; // payload type
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// char_or_die = MyError.Argh; // error
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//
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// 7. 'undefined' coerces to any type (or it wouldn't work!)
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//
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// 8. Compile-time numbers coerce to compatible types.
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//
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// Just about every single exercise program has had an example
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// of this, but a full and proper explanation is coming your
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// way soon in the third-eye-opening subject of comptime.
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//
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// 9. Tagged unions coerce to the current tagged enum.
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//
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// 10. Enums coerce to a tagged union when that tagged field is a
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// a zero-length type that has only one value (like void).
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//
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// 11. Zero-bit types (like void) can be coerced into single-item
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// pointers.
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//
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// The last three are fairly esoteric, but you're more than
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// welcome to read more about them in the official Zig language
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// documentation and write your own experiments.
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const print = @import("std").debug.print;
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pub fn main() void {
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var letter: u8 = 'A';
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const my_letter: ?*[1]u8 = &letter;
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// ^^^^^^^
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// Your type here.
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// Must coerce from &letter (which is a *u8).
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// Hint: Use coercion Rules 4 and 5.
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// When it's right, this will work:
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print("Letter: {u}\n", .{my_letter.?.*[0]});
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}
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