⚡ Strict Types in PHP (declare(strict_types=1))

By default, PHP is a dynamically and weakly typed programming language that attempts to automatically coerce data types when mismatched values are passed into functions or returned from them. Introducing declare(strict_types=1); enforces strict type checking rules, preventing implicit type coercion and throwing a TypeError whenever types do not match expectations.

1️⃣ Weak Typing (Default Behavior)
Without strict types, PHP automatically converts string numbers into integers or floats if a function demands a numeric type.

<?php
// Default mode: Automatic coercion is active
function sum(int $a, int $b): int {
    return $a + $b;
}

// PHP automatically converts "5" string into integer 5
echo sum(5, "10"); // Outputs: 15

2️⃣ Strict Typing (With declare(strict_types=1))
When strict mode is enabled, passing a data type that does not strictly match the type declaration results in an immediate TypeError exception.

<?php
declare(strict_types=1);

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

// Passing string "10" triggers a Fatal TypeError
try {
    echo sum(5, "10");
} catch (TypeError $e) {
    echo "Error: " . $e->getMessage();
    // Output: Argument #2 ($b) must be of type int, string given
}

The strict types directive applies per-file basis for function calls made within that file. It does not affect functions called in other included files unless those files also explicitly declare strict mode at the top.

<?php
declare(strict_types=1);

function calculateTax(float $amount, float $rate): float {
    return $amount * $rate;
}

// Correct usage: both arguments and return type match declared float types strictly
$tax = calculateTax(100.0, 0.18);
echo "Tax: " . $tax; // Outputs: Tax: 18