Immutable objects in PHP?

Question

Is it a good idea to create objects that cannot be changed in PHP?

For example a date object which has setter methods, but they will always return a new instance of

Answer 1

Immutable objects don't have setter methods. Period.

Everyone will expect a setXyz() method to have a void return type (or return nothing in loosely typed languages). If you do add setter methods to your immutable object it will confuse the hell out of people and lead to ugly bugs.