PHP class constructor problem

Question

class upload{
   protected $name;
    protected $sex;

 public function __construct($name='默认值',$sex='默认值'){
     $this->name=$name;
     $this->sex=$sex;
  }
}

Why can’t it be written like this?

 public function __construct($name,$sex){
     $this->name=$name;
     $this->sex=$sex;
  }

Can I also write like this? If there are too many parameters above, what year, horse and month should be written?

public function __construct($opt){
     $this->name=$opt->name;
     $this->sex=$opt->sex;
  }

Why must you add a default value to the constructor, otherwise an error will be reported! ! ! I'm used to writing js, so I don't understand the constructor of php a bit. Explain, is it necessary to assign default values ​​to parameters?

Answer 1

Has nothing to do with constructors.
As long as the parameters of the function are not given default values, you must pass the parameters when using it.

It is not right to say that it is more troublesome than js. In js (before ES6), setting default values ​​for functions is more troublesome than php; so what can I say?

In addition, the third method you mentioned is to pass an object or an array as a parameter. This approach is okay; of course, you can use a loop when assigning values ​​instead of writing them one by one.

Answer 2

1. You don’t need to give a default value. The error you reported here should be because your first parameter was given a default value. Parameters with default values ​​​​should be placed at the back, according to the grammar regulations. (For details, please refer to the document)
2. Pass in Of course the object is also possible

Answer 3

This has nothing to do with the constructor
If you don’t pass parameters when defining the function, an error will be reported

function a($name,$age = 1)
{
}

$name must be passed, $age is not required. $name必传，$age不用。
至于为什么，PHP语法规定As for why, PHP syntax regulations

The PHP syntax does not report an error. Try running it. If PHP reports an error, post the error message

Answer 4

If the PHP function is explicitly specified and the parameters are not given default values, the parameters must be passed when calling. If there is a default value, you can read the default value without passing parameters when calling.

If you find it troublesome to pass parameters explicitly, you can use the func_get_args() function to read the parameters.

After PHP5.6, you can also use the function A(...$args) form to read parameters.

Answer 5

The constructor is the function called by default when you create a new object

The parameters of the function must be passed if there is no default value. This is a grammatical rule

All functions are like this. No matter how many parameters you have, you have to pass them one by one

All the languages ​​I know have this rule

Answer 6

Can you wear an array