Discussion on: Closure Pattern in Zig

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Replies for: The definition for ClosureBind is wrong, since it used comptime this: ClosureScope. The correct definition for ClosureBind should have omitted comp...

Removing comptime from ClosureScope doesn't change anything. ClosureFunc returns a type and is therefore a comptime function and anything you pass to it has to be comptime known and is therefore implicitly also comptime. ClosureFunc is a comptime function generator that binds the function to some static values. It does not generate closures.

You can verify this in your example by passing a variable to TextInRange instead of a literal. Will get the message error: unable to resolve comptime value.

You can't implement closures without an additional state parameter at the closure call site. This is why closures in static languages are always some sort of object.

Andrew Houghton • May 15

In response to your comment I added the following test which confirms your assertion that the presented implementation works only with compile time static values and my misunderstanding of Zig's comptime concept.

test "[Comptime Only Issue]" {

    // Test reuse invocation of the closure.
    var from: u32 = undefined;
    var to: u32 = undefined;

    from = 2;
    to = 5;

    const closure = TextInRange(from, to);

    const text = closure("0123456789");
    print("text = {s}\n", .{text});
}

After further review of the presented implementation and a few minor changes to ClosureType and ClosureBind the above test passes using runtime variables. I'll update the article. Thanks for clarifying Zig's comptime concept.