Why Can\'t I Call Non-Static PHP Methods Using the Double-Colon Syntax?

Calling Non-Static Methods with Double-Colon Syntax

In PHP, it's common to call static methods using the double-colon syntax, such as ClassName::methodName(). However, attempting to invoke a non-static method with this syntax can lead to confusion.

Why Double-Colon Syntax Doesn't Work for Non-Static Methods

Unlike static methods, non-static methods require an instance of the class to operate. When a non-static method is called with ClassName::methodName(), PHP interprets it as a static method, which doesn't make sense for methods that need specific instance variables or access to the $this keyword.

PHP's Loose Typing

PHP handles static and non-static methods differently, but it's important to note that PHP is relatively loose in this regard. Even though calling a non-static method with double-colon syntax is technically incorrect, PHP may still allow it in certain circumstances.

However, this behavior can lead to unexpected results or errors, especially when using strict error reporting. In such cases, PHP will throw an error indicating that the non-static method must be called on an object.

Referencing $this from Non-Static Methods

Interestingly, PHP allows calling a non-static method statically from within another non-static method of the same class. In this case, the $this keyword in the called method will refer to the instance of the calling class.

For example, consider the following code:

class A 
{
    public function test()
    {
        echo $this->name;
    }
}

class C 
{
     public function q()
     {
         $this->name = 'hello';
         A::test();
     }
}

$c = new C;
$c->q(); // prints hello

In this example, the test() method of class A is called statically from the q() method of class C. The $this keyword in test() references the instance of C ($c), allowing the code to access the name property and print "hello."

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