Anonymous function? | Zig Programming Language | Page 1

upbeat ruin Dec 20, 2022, 6:28 AM

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How do folks write anonymous functions in Zig?

I wrote the following this zls seemed to not display any errors.

    root.visitDirs(fn (n: *Node) void {
        if (n.typ == .dir) {
            print("{s}: {d}", .{ n.name, n.totalSize() });
        }
    });

But when I run it, I see this:

main.zig:56:13: error: use of undeclared identifier 'n'
        if (n.typ == .dir) {

n is clearly defined in the parameter list of the function, so I'm guessing I'm writing anonymous functions incorrectly.

urban falcon Dec 20, 2022, 6:29 AM

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simple answer: you can't

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also, zls is not a litmus test for code validity, fair warning :)

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slightly more complex answer: use a struct hack!

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const myFn = struct {
  pub fn myFn(abc: Def) Ghi { ... }
}.myFn;

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not sure if this still works with all the stage2 going on atm but it's how it's always worked :)

upbeat ruin Dec 20, 2022, 6:31 AM

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Oh my, I've used that hack once facepalm I forgot about it. Ugh.

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thanks

upbeat ruin Dec 20, 2022, 6:37 AM

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urban falcon simple answer: you can't

Making sure I understand, you mean there's no such thing as anonymous functions in Zig? They have to be declared with a name?

urban falcon Dec 20, 2022, 6:55 AM

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kinda

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the anonymity isn't really the blocker

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moreso scope issues

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and access to locals

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it's weird

upbeat ruin Dec 20, 2022, 7:23 AM

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Got it.

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So a learning from this is that instead of writing closures that capture state, I need to pass a "context" of sorts down to functions I'm calling, and I can make that context anytype.

#Anonymous function?