How to learn method parameter type declarations

This article will introduce you to the method of learning method parameter type declaration. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.

#No matter what industry you are engaged in, it is now a trend to live and learn, especially those of us who are programmers. It goes without saying that the new technology is not applicable this time. Just by studying the PHP documentation, you will find that there are many knowledge points that you do not really understand, such as the type declaration of this method parameter.

In the last article, regarding the method parameter type constraints of PHP, we said that the type constraints of method parameters are limited to classes, interfaces, arrays or callable callback functions. In fact, this is not rigorous. There is also one in PHP The definition of strict mode. If strict mode is specified, it is also effective to specify an ordinary scalar type for the method parameter type.

Definition of strict mode:

declare (strict_types = 1);

int type

function testInt(int $a)
{
    echo $a, PHP_EOL;
}

testInt(1);
// testInt(1.1); // Fatal error: Uncaught TypeError: Argument 1 passed to testInt() must be of the type int
// testInt('52AABB'); // Fatal error: Uncaught TypeError: Argument 1 passed to testInt() must be of the type int
// testInt(true); // Fatal error: Uncaught TypeError: Argument 1 passed to testInt() must be of the type int

In strict mode, it is obvious that the parameters of this method can only After receiving values ​​of type int, other types cannot be received. Of course, no forced conversion will occur as mentioned in the previous article.

float type

function testFloat(float $a)
{
    echo $a, PHP_EOL;
}

testFloat(1);
testFloat(1.1);
// testFloat('52AABB'); // Fatal error: Uncaught TypeError: Argument 1 passed to testInt() must be of the type int
// testInt(true); // Fatal error: Uncaught TypeError: Argument 1 passed to testInt() must be of the type int

It should be noted here that PHP only has int and float, and float is a superset of int, so integers can be passed here. However, the above testInt(int $a) cannot receive float values ​​such as 1.1. This involves the issue of up and down conversion. Converting to a superset is OK, but converting a superset to a subset is not OK.

string type

function testString(string $a)
{
    echo $a, PHP_EOL;
}

// testString(1);  // Fatal error: Uncaught TypeError: Argument 1 passed to testString() must be of the type string
// testString(1.1);  // Fatal error: Uncaught TypeError: Argument 1 passed to testString() must be of the type string
testString('52AABB');
// testString(true); // Fatal error: Uncaught TypeError: Argument 1 passed to testString() must be of the type string

No need to explain too much. In non-strict mode, if we define a receiving parameter of string type, it can actually be any type. Received as string type, there is no need to talk about the type conversion here. It can be said that the effect of defining the string type in non-strict mode is the same as without any definition. But it's different in strict mode. It really can only receive string content within double quotes or single quotes.

bool type

function testBool(bool $a)
{
    var_dump($a);
}
testBool(true);
testBool(false);
// testBool('52AABB'); // Fatal error: Uncaught TypeError: Argument 1 passed to testBool() must be of the type bool
// testBool(1); // Fatal error: Uncaught TypeError: Argument 1 passed to testBool() must be of the type bool

The same goes for Boolean values. Here we can only receive the values ​​of the true and false keywords.

Learn a new iterable type

Finally, let’s introduce a new guy. In addition to classes, arrays, and callback functions in normal mode, various scalar types in strict mode In addition to the declaration, there is also an iterable type declaration. I believe you can also see it through this word. It is an iterable type.

function testIterable(iterable $iterator)
{
    echo gettype($iterator), ':', PHP_EOL;
    foreach ($iterator as $it) {
        echo $it, PHP_EOL;
    }
}

testIterable([1, 2, 3]);
testIterable(new ArrayIterator([1, 2, 3]));
// Generator对象
testIterable((function () {
    yield 1;
    yield 2;
    yield 3;
})());
// testIterable(1); // Fatal error: Uncaught TypeError: Argument 1 passed to testIterable() must be iterable

Yes, it includes arrays, classes that implement the iterator interface, and generator-related content. That is, all the contents that can be iterated by foreach can be passed. The generator itself will be a Generator object, and in this article about learning the use of PHP generators, we have already seen the contents of this Generator object, which itself also implements the Iterator interface.

Summary

As mentioned at the beginning, it turns out that our grammar will be so different in strict mode. This time I really learned a lot. . We still have a long way to learn, and I hope you can continue to pay attention and work hard together! !

Test code:

https://github.com/zhangyue0503/dev-blog/blob/master/php/202003/source/%E5%86%8D%E6%AC%A1%E5%AD%A6%E4%B9%A0%E6%96%B9%E6%B3%95%E5%8F%82%E6%95%B0%E7%B1%BB%E5%9E%8B%E5%A3%B0%E6%98%8E.php

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