Question: How to pass function?

[kanatapple]

Hi, How can I pass a function to msg_send and call it?
For example, I want to pass a function to the completionHandler of setCookie method in WKHTTPCookieStore like in the code below.

// https://developer.apple.com/documentation/webkit/wkhttpcookiestore/2882007-setcookie?language=objc
msg_send![http_cookie_store, cookie: cookie_data, completionHandler: function];

I don't know how to define function.

I'm actually using objc, but this community is more active so I asked here.

[madsmtm]

The completionHandler argument is not a function, rather, it is a "block" (see this for details, essentially the C-equivalent of a Rust dyn Fn closure).

So to call it, you'd do something like this:

use block2::{Block, ConcreteBlock}; // or the old `block` crate

let handler = ConcreteBlock::new(|| {
    // Code to run on completion.
    // This closure can capture values, but since `completionHandler` is executed asynchronously, the captured
    // values must be `Send + Sync`.
});
// Put the block on the heap
let handler = handler.copy();
// Ensure that the block has the correct type (no arguments, `void` return type)
let handler: &Block<(), ()> = &handler;

let _: () = unsafe { msg_send![http_cookie_store, cookie: cookie_data, completionHandler: handler] };

[madsmtm]

(I know that the API that the block2 crate exposes is not really that nice to work with, I am working on improving this, see #168)

[kanatapple]

Thanks. I will try.

[kanatapple]

It's working as expected.
Thank you.

[silvanshade]

@madsmtm Is the example above still how one is supposed to pass a block as an argument? It doesn't seem to work with the published crates (block2 = "0.1.6" and icrate = "0.0.1").

With the following simplified example, I get an error:

EDIT: Oh, I just realized the issue was due to using an outdated/conflicting versions of block2 with icrate. Working now :)