Scalar type declarations in PHP allow you to specify the type of a function's parameters and return values, ensuring type safety and consistency within your code. PHP supports two main types of scalar type declarations: coercive and strict.

Coercive Type Declarations

Coercive type declarations allow PHP to automatically convert the provided argument to the specified type if possible. These declarations are indicated by specifying the type name (e.g., int, float, string, bool) directly in the function definition.

Function with Coercive Type Declarations

php
<?php
        function addNumbers(int $a, float $b): float {
            return $a + $b;
        }
        
        echo addNumbers(5, 3.5); // Outputs: 8.5
        ?>
        

In the example:

• int $a: Specifies that the parameter $a must be an integer. PHP will attempt to convert the provided value to an integer if possible.
• float $b: Specifies that the parameter $b must be a floating-point number. Again, PHP will attempt conversion if necessary.

Strict Type Declarations

Strict type declarations enforce type checking strictly without automatic type conversion. This ensures that the function parameters and return values are of the specified types, and PHP throws a TypeError if the provided types do not match.

To enable strict type declarations for a file, add the following declaration at the beginning of your PHP script:

php
<?php
        declare(strict_types=1);
        

Example Using Strict Type Declarations

php
<?php
        declare(strict_types=1);
        
        function addNumbers(int $a, float $b): float {
            return $a + $b;
        }
        
        echo addNumbers(5, 3.5); // Outputs: 8.5
        echo addNumbers(5, "3.5"); // TypeError: Argument 2 passed to addNumbers() must be of the type float
        ?>
        

In the strict mode example:

• Passing "3.5" as the second argument causes a TypeError because "3.5" is a string, not a float.

Summary:

Scalar type declarations in PHP (int, float, string, bool) allow you to enforce type safety in function parameters and return values. Coercive type declarations (default behavior) allow type conversion where possible, while strict type declarations enforce strict type checking without conversion. Understanding and using these declarations appropriately can help improve the reliability and maintainability of your PHP applications.