Introducing new features from php7.3 to php7.4

1. Object attributes now support type declaration

<?php class User {
    public int $id;
    public string $name;
}
?>

In the above example, $id will be forced to be converted to integer type, $name is String type

Recommended (free):PHP7

2. Arrow function

Now the arrow function will Provide a short syntax for defining functions whose value declarations are unclear within the scope

<?php $factor = 10;
$nums = array_map(fn($n) => $n * $factor, [1, 2, 3, 4]);
// $nums = array(10, 20, 30, 40);
?>

3, limited return type covariance and parameter type covariance (Google Translate)

The following code will Will run

<?php class A {}
class B extends A {}

class Producer {
    public function method(): A {}
}
class ChildProducer extends Producer {
    public function method(): B {}
}
?>

Full diff support is only provided when using autoloading. Within a single file, only non-cyclic type references can be used because all classes must be available before being referenced

4, Null merge assignment operator

<?php $array[&#39;key&#39;] ??= computeDefault();
// is roughly equivalent to
if (!isset($array[&#39;key&#39;])) {
    $array[&#39;key&#39;] = computeDefault();
}
?>

5, Unpacking inside arrays (Google The translation is to unpack inside the array. See if this is wrong, use English first)

<?php $parts = [&#39;apple&#39;, &#39;pear&#39;];
$fruits = [&#39;banana&#39;, &#39;orange&#39;, ...$parts, &#39;watermelon&#39;];
// [&#39;banana&#39;, &#39;orange&#39;, &#39;apple&#39;, &#39;pear&#39;, &#39;watermelon&#39;];
?>

6. Numeric character separator

Numeric characters can include underscores between numbers.

<?php 6.674_083e-11; // float
299_792_458;   // decimal
0xCAFE_F00D;   // hexadecimal
0b0101_1111;   // binary
?>

7. Weak references

Weak references allow the programmer to retain a reference to an object that cannot be prevented from being destroyed does not prevent the object from being destroyed.)

8. Allow exceptions __toString()

can now be thrown through __toString() Exceptions, which in previous versions would have resulted in a fatal error, existing string conversions that could have resulted in a fatal error have been converted to throw exceptions.

We will look at the rest of the expansion later

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