PHP calls method parameters in front of...

In PHP, we can achieve variable number of parameter passing by adding three dots (...) in front of the method parameters. This method is also called "variable parameter list" or "indefinite number of parameters".

Let’s take a look at the specific usage and details.

Basic syntax

In PHP, when we declare a method, we can add three dots in front of the method parameter to indicate that the parameter is variable, for example:

function myFunc(...$args) {
  // 执行代码
}

In this code, the three dots in front of the $args parameter indicate that it is a variable-length parameter list. This means that when calling the myFunc() method, we can pass any number of parameters, and these parameters will be placed in the $args array.

Usage method

When using variable-length parameters, we can call it in the following way:

myFunc(1, 2, 3, 4);

In this example, we call myFunc()# Four parameters are passed in ##, and they will be placed in the $args array.

It should be noted that when using variable parameters, we must ensure that these parameters are all of the same type, otherwise errors may occur.

Practical Application

Variable parameter lists are widely used in actual development, especially in the development of function libraries or frameworks.

Suppose we need to write a function that can extract specified key-value pairs from multiple arrays. The code probably looks like this:

function extractByKey($key, ...$arrays) {
  $result = array();

  foreach ($arrays as $array) {
    if (array_key_exists($key, $array)) {
      $result[] = $array[$key];
    }
  }

  return $result;
}

In this example, we first define A

$key variable indicating the key name to be extracted. Then we use a variadic argument list to pass the array that needs to be extracted.

In the function body, we first create an empty

$result array to represent the final extracted result. Then we iterate through all the arrays passed in the variable parameters to determine whether $key exists in the array. If it exists, we add the value corresponding to $key in the array to the $result array.

Finally, we return the

$result array, which contains the specified key-value pairs extracted from all arrays.

Summary

In PHP, the function of a variable parameter list can be achieved by adding three dots (...) before the method parameters. This method is widely used in actual development and can flexibly pass any number of parameters when calling functions.

It should be noted that when using variable parameters, we must consider the type of parameters to ensure that they are all of the same type.

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