60 lines
1.5 KiB
Zig
60 lines
1.5 KiB
Zig
//
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// Another common problem is a block of code that could exit in multiple
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// places due to an error - but that needs to do something before it
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// exits (typically to clean up after itself).
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//
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// An "errdefer" is a defer that only runs if the block exits with an error:
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//
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// {
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// errdefer cleanup();
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// try canFail();
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// }
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//
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// The cleanup() function is called ONLY if the "try" statement returns an
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// error produced by canFail().
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//
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const std = @import("std");
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var counter: u32 = 0;
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const MyErr = error{ GetFail, IncFail };
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pub fn main() void {
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// We simply quit the entire program if we fail to get a number:
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var a: u32 = makeNumber() catch return;
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var b: u32 = makeNumber() catch return;
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std.debug.print("Numbers: {}, {}\n", .{ a, b });
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}
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fn makeNumber() MyErr!u32 {
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std.debug.print("Getting number...", .{});
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// Please make the "failed" message print ONLY if the makeNumber()
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// function exits with an error:
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errdefer std.debug.print("failed!\n", .{});
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var num = try getNumber(); // <-- This could fail!
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num = try increaseNumber(num); // <-- This could ALSO fail!
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std.debug.print("got {}. ", .{num});
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return num;
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}
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fn getNumber() MyErr!u32 {
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// I _could_ fail...but I don't!
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return 4;
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}
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fn increaseNumber(n: u32) MyErr!u32 {
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// I fail after the first time you run me!
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if (counter > 0) return MyErr.IncFail;
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// Sneaky, weird global stuff.
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counter += 1;
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return n + 1;
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}
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