Chaining question

[ghost]

I have an array of items of variable length where I want to process each item by the same function after the previous promise has resolved. I just can't figure out how to code it, I keep ending up thinking in loops while I guess I shouldn't:

$items = array(...variable number of items in here...);

$this->doSomethingAsyncAndReturnAPromise($firstItem)->then(
    function () {
        $this->doSomethingAsyncAndReturnAPromise($secondItem)->then(     
            ... and so on for all the remaining $items
        );
    }
);

Can anyone point me in the right direction how to do this?

[jsor]

You can use React\Promise\reduce if you want to run the tasks in sequence with no overlap:

React\Promise\reduce($items, [$this, 'doSomethingAsyncAndReturnAPromise'])->then(function() {
    echo "All done";
});

If they can run in parallel, use React\Promise\map:

React\Promise\map($items, [$this, 'doSomethingAsyncAndReturnAPromise'])->then(function() {
    echo "All done";
});

[ghost]

Great info, I was looking for use cases for these two functions already. It was not very clear to me from the documentation how to use them.

Many thanks, reduce() it is.

[jsor]

They both work exactly like PHP's array_map and array_reduce with the addition that the values of the input array can be promises and the callbacks can return promises.

In this case, we're "abusing" reduce() for your use case. Since the callback must receive the return value of the previous iteration, reduce() takes care of running in sequence.