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