Design pattern foundation (1)

The purpose of design patterns is: reuse.

In object-oriented, a class is a code template used to generate objects, and a design pattern is a code template used to solve common problems.

Following such a template, we can design excellent code quickly.

Note that design patterns are just templates, not specific codes.

It is for code reuse and increase maintainability .

When learning design patterns, there are several concepts that make me hard to accept. This may be the confinement from procedural programming to object-oriented programming.

Suppose there is such an object:

class Person
{
    private $name = 'Human';

    public function getName()
    {
        return $this->name;
    }
}

1 Variable storage object

Don't think that variables can only store integer numbers, arrays and strings. Variables can also store objects:

$man = new Person;
echo $man->getName();

2 Passing object parameters

If another class uses the properties or methods of the Person class, just go directly into it:

class Student
{
    public function __construct($person)
    {
        echo $person->getName();
    }
}

// 传递对象，最后输出字符串“Human”
$jack = new Student(new Person);

But this has a small problem, when it new Student()is not passed to an Personobject, as follows,

$jack = new Student('abc');

The program will report an error. So there is a third way to limit the type of parameters.

3 Limit the type of passed parameters

When passing parameters, limit the type of the parameter, write like this:

class Student
{
    public function __construct(Person $person)
    {
        echo $person->getName();
    }
}

// 传递对象，
$jack = new Student(new Person);

In this way, the passed new Student()parameter must be Personan instance.

4 Save objects with class attributes

There is also a frequently used method, which is to save an object or a collection of objects with a class attribute. as follows:

class Life
{
    public $persons = [];
    
    public function addPerson(Person $person)
    {
        $this->persons[] = $person;
    }
}

$class = new Life();
$class->addPerson(new Person);
$class->addPerson(new Person);

var_dump($class->persons);

output value:

array(2) {
  [0]=>
  object(Person)#2 (1) {
    
    
    ["name":"Person":private]=>
    string(5) "Human"
  }
  [1]=>
  object(Person)#3 (1) {
    
    
    ["name":"Person":private]=>
    string(5) "Human"
  }
}

5 Summary

Object-oriented design patterns are formed after some combination of the above situation.

Therefore, understanding the relationship between classes is the key.

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