Well, FWIW worth that&#x27;s not the primary reason I like those languages. It&#x27;s the safety.<p>After some experience with immutable data structures, you know how to make them efficient. For example most of the time you don&#x27;t need to copy that much data - if you need to change a small part of a large data structure, you arrange it so you can re-use (re-point to) the parts you didn&#x27;t change. On average you should be able to reduce your cost down to O(log(n)) which usually is &quot;good enough&quot;.<p>That is the correct trade-off IMO - have a newbie start off writing safe code, that gets quicker and less memory intensive with experience. Not start off be blazing quick but unsafe, then add the safety with experience.<p>Did you know Rust (which defaults to immutable) is currently head-to-head with C in Debian&#x27;s &quot;fastest languages&quot; comparison?<p><a href="https:&#x2F;&#x2F;benchmarksgame.alioth.debian.org&#x2F;u64q&#x2F;rust.html" rel="nofollow">https:&#x2F;&#x2F;benchmarksgame.alioth.debian.org&#x2F;u64q&#x2F;rust.html</a>