4 ms·

Because you cannot have loops in an immutable universe? Sure, you can map functions, but sometimes loops are fun too.

• tialaramex 4y ago
  It's actually better if you have immutability here, languages which try to instead have a single variable for the values, mutating that variable each time around the loop, get into some trouble. Compare Rust's for loop: for k in 0..10 { // k is an immutable variable, brought into existence for one iteration // next time around the loop that's a different immutable k } Versus the C for loop: for (k = 0; k < 10; ++k) { // k is a long-lived mutable variable, we can change k inside the loop and it'll remember! } We can tell Rust we want a mutable variable, if we want, but it's not the same: for mut k in 0..10 { // k is a mutable variable... // but still brought into existence for each iteration // changing will work in this scope... but it won't last }
  • widforss 4y ago
    Cool, I didn't know that Rust did that (or have forgotten)! But it sure looks like a map where we throw away the result. What I mean with that is that the loop construct must be served the iterations from an iterator, which may or may not use immutable data. I don't think you can make an immutable while loop, for example? EDIT: Also, you better have a side-effect in that construct, otherwise it has no effect, right?
• qwerty456127 4y ago
  I mean both ways should be available. It generally is reasonable to support mutable variables but immutable values should be supported as well. E.g. Scala has 2 separate keywords: var and val (the difference is you can't assign a val again once it is initialized). I want the same in C#, Python and other languages.
  • cerved 4y ago
    also JS let/const