> It's just because OOP relies directly on mutable state > (in Imperative Languages, which are the most common OOP implementation). > The Object's methods you

> It's just because OOP relies directly on mutable state > (in Imperative Languages, which are the most common OOP implementation). > The Object's methods you call is supposed to mutate the current self or this. > A lot of complexity will be needed to keep all threads correctly updated and synchronized. Nothing prevents you to create immutable objects in OOP language. Immutability is the key here, not the functional languages.