How does calling function pointers work?

[Rene Zwanenburg]

On Monday, 12 November 2018 at 16:29:24 UTC, helxi wrote:
> On Monday, 12 November 2018 at 16:25:13 UTC, Rene Zwanenburg 
> wrote:
>> Idk where you got that syntax from, but there's no syntactic 
>> difference between calling normal functions and function 
>> pointers:
>
> import std.stdio;
> import std.concurrency;
> import core.thread;
>
> void worker(int firstNumber) {
>     foreach (i; 0 .. 4) {
>         Thread.sleep(500.msecs);
>         writeln(firstNumber + i);
>     }
> }
>
> void main() {
>     foreach (i; 1 .. 3) {
>         spawn(&worker, i * 10);
>     }
> }
>
>
> Looks like worker needs an int and spawn(&worker, i * 10) seems 
> to feed it's second arg to worker(?)

That's right. spawn() is a function in the standard library that 
takes a function pointer, and all the arguments to pass to that 
function. It's a bit unusual in that regard: normally when using 
function pointers the arguments are provided by the code that 
receives the function pointer. Internally, spawn will call the 
function pointer just like I did in my example, but on another 
thread.

Here's an example where a function pointer is passed around with 
the arguments provided by the callee:
https://run.dlang.io/is/ArCN5t