Strict Types Type Coercion Failure

Why This Happens

When declare(strict_types=1) is set at the top of a file, PHP enforces exact type matching for function arguments and return values. Without it, PHP silently coerces '42' to integer 42. With strict types, the string '42' is not accepted where an int is required.

The Problem

<?php
declare(strict_types=1);

function add(int $a, int $b): int {
    return $a + $b;
}

$result = add('5', '3'); // TypeError: string given, int expected

The Fix

<?php
declare(strict_types=1);

function add(int $a, int $b): int {
    return $a + $b;
}

$a = (int) $_GET['a']; // Explicit cast
$b = (int) $_GET['b'];
$result = add($a, $b);

Step-by-Step Fix

1. 1

   Check strict_types declaration

   Look at the top of the file for declare(strict_types=1). This enables strict type checking for that file's function calls.

2. 2

   Cast values explicitly

   Cast variables to the correct type before passing them: (int), (float), (string), (bool), (array).

3. 3

   Validate input types

   For user input that is always a string, validate and cast to the required type early in your processing pipeline.