How to Use PHP’s is_callable() to Safely Check Functions and Methods

In PHP, you can determine whether a function or method can be called by using the is_callable() function.

The is_callable() function takes a single argument—the variable to check—and returns a boolean: true if the variable is callable, otherwise false.

Below is a simple example:

<?php

function testFunction() {
    echo "Hello, world!";
}

$functionName = 'testFunction';
$methodName   = 'nonExistent';

echo "functionName is callable? ";
if (is_callable($functionName)) {
    echo "Yes";
} else {
    echo "No";
}
echo "<br>";

echo "methodName is callable? ";
if (is_callable($methodName)) {
    echo "Yes";
} else {
    echo "No";
}
?>

The script defines a function testFunction() and assigns its name and a non‑existent method name to $functionName and $methodName respectively. It then uses is_callable() to test each variable, outputting “Yes” for the existing function and “No” for the missing method.

functionName is callable? Yes
methodName is callable? No

This demonstrates that is_callable() can verify functions, methods, class constructors, and static methods before invoking them, helping you write more robust PHP code.