76 lines
2.0 KiB
Zig
76 lines
2.0 KiB
Zig
//
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// Using `catch` to replace an error with a default value is a bit
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// of a blunt instrument since it doesn't matter what the error is.
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//
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// Catch lets us capture the error value and perform additional
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// actions with this form:
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//
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// canFail() catch |err| {
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// if (err == FishError.TunaMalfunction) {
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// ...
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// }
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// };
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//
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const std = @import("std");
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const MyNumberError = error{
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TooSmall,
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TooBig,
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};
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pub fn main() void {
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// The "catch 0" below is a temporary hack to deal with
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// makeJustRight()'s returned error union (for now).
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var a: u32 = makeJustRight(44) catch 0;
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var b: u32 = makeJustRight(14) catch 0;
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var c: u32 = makeJustRight(4) catch 0;
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std.debug.print("a={}, b={}, c={}\n", .{ a, b, c });
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}
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// In this silly example we've split the responsibility of making
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// a number just right into four (!) functions:
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//
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// makeJustRight() Calls fixTooBig(), cannot fix any errors.
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// fixTooBig() Calls fixTooSmall(), fixes TooBig errors.
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// fixTooSmall() Calls detectProblems(), fixes TooSmall errors.
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// detectProblems() Returns the number or an error.
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//
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fn makeJustRight(n: u32) MyNumberError!u32 {
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return fixTooBig(n) catch |err| {
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return err;
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};
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}
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fn fixTooBig(n: u32) MyNumberError!u32 {
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return fixTooSmall(n) catch |err| {
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if (err == MyNumberError.TooBig) {
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return 20;
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}
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return err;
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};
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}
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fn fixTooSmall(n: u32) MyNumberError!u32 {
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// Oh dear, this is missing a lot! But don't worry, it's nearly
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// identical to fixTooBig() above.
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//
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// If we get a TooSmall error, we should return 10.
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// If we get any other error, we should return that error.
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// Otherwise, we return the u32 number.
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return detectProblems(n) catch |err| {
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if (err == MyNumberError.TooSmall) {
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return 10;
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}
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return err;
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};
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}
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fn detectProblems(n: u32) MyNumberError!u32 {
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if (n < 10) return MyNumberError.TooSmall;
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if (n > 20) return MyNumberError.TooBig;
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return n;
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}
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