PHP: bool vs boolean type hinting

问题

I've been trying to use type hinting more in PHP. Today I was writing a function that takes a boolean with a default parameter and I noticed that a function of the form

function foo(boolean $bar = false) {
    var_dump($bar);
}

actually throws a fatal error:

Default value for parameters with a class type hint can only be NULL

While a function of the similar form

function foo(bool $bar = false) {
    var_dump($bar);
}

does not. However, both

var_dump((bool) $bar);
var_dump((boolean) $bar);

give the exact same output

:boolean false

Why is this? Is this similar to the wrapper classes in Java?

回答1:

http://php.net/manual/en/functions.arguments.php#functions.arguments.type-declaration

Warning
Aliases for the above scalar types are not supported. Instead, they are treated as class or interface names. For example, using boolean as a parameter or return type will require an argument or return value that is an instanceof the class or interface boolean, rather than of type bool:
<?php
function test(boolean $param) {}
test(true);
?>
The above example will output:

Fatal error: Uncaught TypeError: Argument 1 passed to test() must be an instance of boolean, boolean given

So in a nutshell, boolean is an alias for bool, and aliases don't work in type hints.
Use the "real" name: bool

There are no similarity between Type Hinting and Type Casting.

Type hinting is something like that you are telling your function which type should be accepted.

Type casting is to "switching" between types.

The casts allowed are:

(int), (integer) - cast to integer
(bool), (boolean) - cast to boolean
(float), (double), (real) - cast to float
(string) - cast to string
(array) - cast to array
(object) - cast to object
(unset) - cast to NULL (PHP 5)

In php type casting both (bool) and (boolean) are the same.

来源：https://stackoverflow.com/questions/44009037/php-bool-vs-boolean-type-hinting

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php

boolean

default-value

type-hinting