传递给array_filter时参数丢失

Question

    foreach( $items as $item) {
    $taskid = (int) $goal['goal_id'];
    $items[$i]['tasks'] = array();
    $items[$i]['tasks'] = array_filter($tasks, function($task, $taskid){    
    return $task['task_id'] == $taskid;
    });

Why is $taskid not being passed to the array_filter function, it returns null if echoed from within but if echoed just after it is set it gives the correct value e.g.

    foreach( $items as $item) {
    $taskid = (int) $goal['goal_id'];
    echo $taskid;

Will return whatever the integer is

The return part of the function also works if I manually set a value i.e

    return $task['task_id'] == 2;

Guidance appreciated

Answer 1

The issue is variable scope and function arguments.

First, array_filter expects a function with a single argument, that argument is the value in the position in the array. It doesn't handle keys.

You set $taskid = (int) $goal['goal_id']; outside of the anonymous function, and you have a local variable of the same name, which is null because array_filter only passes one argument.

foreach( $items as $item) {
  $taskid = (int) $goal['goal_id'];
  $items[$i]['tasks'] = array();
  # Per the OP, you can pass the necessary variable in via 'use'
  $items[$i]['tasks'] = array_filter($tasks, function($task) use($taskid){
    return $task['task_id'] == $taskid;
  });
}