What are the PHP function parameter types?

PHP function parameter types include scalar types (integers, floating point numbers, strings, Boolean values, null values), composite types (arrays, objects) and special types (callback functions, variable parameters). Functions can automatically convert parameters of different types, but they can also force specific types through type declarations to prevent accidental conversions and ensure parameter correctness.

PHP function parameter types

In PHP, function parameters can have the following data types:

Scalar type:

• integer
• float
• string
• boolean
• null

Composite type:

##array
• object

Special type:

callback
• ... (variable number of parameters)

Actual case

Consider the following Function:

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

This function accepts two integer parameters

$a and $b, and returns their sum. Let's go through some examples to understand how PHP checks function parameter types:

echo sum(1, 2); // 输出: 3
echo sum('1', '2'); // 输出: 12 (隐式转换字符串为整数)
echo sum(1.5, 2.5); // 输出: 4 (隐式转换浮点数为整数)
echo sum(null, 1); // 输出: 1 (null 转换为 0)

As you can see, PHP automatically does type conversion to allow different parameter types to be used together. However, in some cases you may need to enforce a specific type:

function checkAge(int $age) {
  // ...
}

By declaring

$age as an integer type, the function will only accept integer arguments. This helps prevent accidental type conversions and forces developers to provide the correct types.

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