Properties of the PHP class

Why does it make a mistake to define values for the properties of the class?
my thinking is because the property can not allocate memory space, I hope you greatly explain it?

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Why does it make a mistake to define values for the properties of the class?
my thinking is because the property can not allocate memory space, I hope you greatly explain it?

Read more about the documentation.

A variable in a property can be initialized, but the initialized value must be a constant, where a constant is a PHP script that can get its value at compile time without relying on the information at run time to evaluate it.

http://php.net/manual/zh/language.oop5.properties.php

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