![barrier gate](http://blog.omelak.com/wp-content/uploads/2021/11/barrier_gate.jpg)
To ensure the class property will never be modified/changed by itself or children or external calls we can now use a readonly
prefix to class property declaration like so: public readonly string $propertyName = 'thisValueWillNeverChange;
. The only place when we could override the readonly variable is inside the class constructor.