If you looked at the arrays walkthrough,
you learned how you can use for loops to walk
over the contents of an array.
While the for loop is powerful, in some instances you may want to allow your own custom types and objects to be used in a for loop.
If you look at the __iterate__ method in std/types/array.para you'll see how the Array type handles for loops.
// std/types/array.para
func __iterate__(self, cb: Func) {
let remaining = self.len();
let len = self.len();
while remaining != 0 {
let index = len - remaining;
cb(self[index]);
remaining -= 1;
}
}The cb parameter is a callback function which for internally uses to hand off execution to the block that was provided for the for loop.
You can think of this as a generator of sorts if you're familiar with that from other languages.