PHP OOP Private Property Assignment Wonder

PHP OOP Private Property Assignment Puzzle
Recently found in class to assign a value to a private variable call the function will be error, not its interpretation, OOP, novice, please master explanation?

Class Test extends Controller {
    Test
   Private $test = count (' csdn ');
}

Parse error:syntax Error, unexpected ' (', expecting ', ' or ';
------Solution--------------------
This is not the reason for the private property
Instead, the class attribute cannot be given an indeterminate value when declaring!

------Solution--------------------

Define (' TEST ', strlen (' csdn '));
Class Test extends Controller {
    Test
   Private $test = test;
}

It's possible to write like this.

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