What is the array_is_list() method in PHP?

Overview

In PHP, we primarily use two types of arrays. These two arrays are the index array and associative array. Either of these arrays can be a list.

What makes an array a list?

We consider an array a list if its keys consist of consecutive numbers from 0 to the size of the array minus the value 1. If the keys of an array are 0,1,2,3,4 until the last array index consecutively, then an array is a list.

The array_is_list() method

The array_is_list() method will check if an array is a list or not and will return the appropriate boolean value to that effect. Therefore, if the array is not a list, a false is returned, and if a true is returned, an array is a list. This function only works on PHP version 8.1 and later.

Syntax

The syntax of the method is as follows:

array_is_list($array_value)

Parameters

  • ＄array_value: We’ll use this array to check if it’s a list.

Return

The function will return an integer 1 if it evaluates as true and an empty value if it evaluates as false.

Code

The code snippet below shows different arrays which are checked for being a list or not.

<?php
//checking if an empty array is a list 
if(array_is_list([])){
  echo "true \n";
}; 
//check if this index array is a list
if(array_is_list(['apple', 2, 3])){
  echo "true \n";
}
// The keys are not in the correct order and doesn't start at zero
if(array_is_list([1 => 'apple', 0 => 'orange']) === false){
   echo "false \n"; // false
}
// This array contains Non-integer keys
if (array_is_list([0 => 'apple', 'foo' => 'bar']) === false)
{
    echo  "false \n";
}  
// Non-consecutive keys
if(array_is_list([0 => 'apple', 2 => 'bar'])=== false){
  echo "false \n";
}; 
?>

Explanation

  • Line 4: We’ll use the if statement to check if an empty array is a list or not and print the value.

  • Line 9: We check if this index array is a list.

  • Line 14: We use an array whose keys are not in the correct order and don’t start at zero, then check if it is a list or not.

  • Line 19: We use the if statement to check if the array_is_list() method will evaluate true on Non-integer keys.

  • Line 24: The array here contains the Non-integer keys. Therefore, it will not evaluate as a list, and the if condition will evaluate as false.

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