PHP scalar type and return value type declaration

Scalar type declaration

By default, all PHP files are in weak type checking mode .

PHP 7 adds the feature of scalar type declaration. There are two modes for scalar type declaration:

  • Forced mode (default)
  • Strict mode

Scalar type declaration syntax format:

declare(strict_types=1);

The code specifies the value of strict_types (1 or 0), 1 Indicates strict type checking mode, which applies to function calls and return statements; 0 indicates weak type checking mode.

The type parameters that can be used are:

  • #int

  • ##float

  • bool

  • string

  • interfaces

  • array

  • callable

Force mode example

Example

<?php
// 强制模式
function sum(int ...$ints)
{
   return array_sum($ints);
}
print(sum(2, '3', 4.1));
?>

The execution output of the above program is:

9
Instance summary Convert parameter 4.1 into an integer 4 and then add it.

Strict Mode Example

Example

<?php
// 严格模式
declare(strict_types=1);
function sum(int ...$ints)
{
   return array_sum($ints);
}
print(sum(2, '3', 4.1));
?>

The above program uses strict mode, so if there is an inappropriate integer type in the parameter, an error will be reported, execute The output result is:

PHP Fatal error: Uncaught TypeError: Argument 2 passed to sum() must be of the type integer, string given, called in……
Return type declaration

PHP 7 adds support for return type declaration, which specifies the type of function return value.

The return types that can be declared are:

  • #int

    • ##float

    • bool

    • string

    • interfaces

    • array

    • callable

    • Return type declaration instance

In the instance, the return result is required to be an integer:

Instance
<?php
declare(strict_types=1);
function returnIntValue(int $value): int
{
   return $value;
}
print(returnIntValue(5));
?>

The execution output of the above program is:

5
Return type declaration error example

Example
<?php
declare(strict_types=1);
function returnIntValue(int $value): int
{
   return $value + 1.0;
}
print(returnIntValue(5));
?>

Since the above program adopts strict mode, the return value must be int, but the calculation result is float, so an error will be reported. The execution output result is:

Fatal error: Uncaught TypeError: Return value of returnIntValue() must be of the type integer, float returned...