Closures in array functions in PHP - Step-by-Step Execution

Concept Flow - Closures in array functions

Define array

↓

Define closure function

↓

Pass closure to array function

↓

Array function calls closure on each element

↓

Closure processes element and returns result

↓

Array function collects results

↓

Output final array

This flow shows how a closure (anonymous function) is defined and passed to an array function, which calls it on each element and collects the results.

Execution Sample

PHP

<?php
$numbers = [1, 2, 3, 4];
$squares = array_map(function($n) { return $n * $n; }, $numbers);
print_r($squares);
?>

This code uses a closure with array_map to square each number in the array.

Execution Table

Step	Array Element	Closure Input	Closure Output	Collected Result
1	1	1	1	[1]
2	2	2	4	[1, 4]
3	3	3	9	[1, 4, 9]
4	4	4	16	[1, 4, 9, 16]
Exit	-	-	-	All elements processed, array_map returns final array

💡 All elements processed, array_map returns final array

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	Final
$numbers	[1, 2, 3, 4]	[1, 2, 3, 4]	[1, 2, 3, 4]	[1, 2, 3, 4]	[1, 2, 3, 4]	[1, 2, 3, 4]
$n (closure input)	-	1	2	3	4	-
Closure output	-	1	4	9	16	-
$squares	[]	[1]	[1, 4]	[1, 4, 9]	[1, 4, 9, 16]	[1, 4, 9, 16]

Key Moments - 3 Insights

Why does the closure receive each element of the array one by one?

Because array_map calls the closure on each element individually, as shown in the execution_table rows 1 to 4.

What happens if the closure does not return a value?

array_map will collect null for that element, so the output array will have nulls in those positions.

Is the original array modified by array_map?

No, the original array ($numbers) stays the same, array_map returns a new array ($squares) as shown in variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table, what is the closure output when the array element is 3?

A 9

B 6

C 3

D None

💡 Hint

Check step 3 in the execution_table where Array Element is 3.

At which step does the collected result first contain the value 4?

A After step 1

B After step 3

C After step 2

D After step 4

💡 Hint

Look at the Collected Result column in execution_table after each step.

If the closure returned $n + 1 instead of $n * $n, what would be the collected result after step 4?

A [1, 4, 9, 16]

B [2, 3, 4, 5]

C [1, 2, 3, 4]

D [0, 1, 2, 3]

💡 Hint

Think about adding 1 to each element instead of squaring it, then check variable_tracker for original values.

Concept Snapshot

Closures in array functions:
- Define an anonymous function (closure) inline.
- Pass it to array functions like array_map.
- The closure runs on each array element.
- array_map collects and returns new array of results.
- Original array stays unchanged.

Full Transcript

This visual trace shows how closures work with array functions in PHP. We start with an array of numbers. We define a closure that squares a number. We pass this closure to array_map, which calls it on each element one by one. Each closure call takes the element as input and returns its square. array_map collects these results into a new array. The original array remains unchanged. The execution table tracks each step, showing input, output, and collected results. The variable tracker shows how variables change after each step. Key moments clarify common confusions about closure inputs, return values, and array immutability. The quiz tests understanding by referencing the execution steps and variable states.