Not really. You can copy the new parts and reference the old, garbage collect dead things, etc. At least in languages where immutability is a core tenet vs stuc

Not really. You can copy the new parts and reference the old, garbage collect dead things, etc. At least in languages where immutability is a core tenet vs stuck on as an after thought. Is it as fast mutable everything? No, some copy must happen, but is a mutable-standard languages as fast as raw hand tuned asm? Also (probably) no, but the trade offs are worth it. It likely matters a lot less than you think unless you're writing actually performance critical tight loop code vs just thinking about performance.