How to Safely Check Callability in PHP with is_callable()

In PHP you can determine whether a function or method can be invoked by using the built-in is_callable() function. is_callable() accepts a single argument – the variable to test – and returns true if it is callable, otherwise false.

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 testFunction(), assigns its name to $functionName, and assigns a non‑existent name to $methodName. is_callable($functionName) returns true because the function exists, while is_callable($methodName) returns false.

functionName is callable? Yes
methodName is callable? No

Beyond simple functions, is_callable() can also verify class constructors and static methods, making it useful for writing more robust code that checks callability before invoking a routine.

Overall, is_callable() is a handy PHP utility for preventing runtime errors by confirming that a variable represents an executable function or method.