[mont_tag]

> Even the JS standard library struggles with this. You just have to remember that .sort() modifies the array in place

ISTM that there are almost always some kinds of mutable data structures present in non-trivial programs. And outside of the program, you have databases to directories of files that get mutated by users or other parts of a program. I think this is just a fact of life.

[magicalhippo]

The point isn't that there's mutability, it's to be able to easily identify where it is and where it is not.

Languages which lack the tools to do this are just harder to reason about, at least for me.

In the JS example, as a non-JS coder, I would expect that a sort function that returns nothing/void would sort in-place, while a sort function that returns an array would return a sorted copy. I would not expect it to sort in-place and return it.

However in C++ I could easily see from the function definition that it might be doing that, because a sort that returns a copy would take a const reference for the input array. So if I came across a sort function which took a non-const reference as input I'd be able to at least suspect it's doing it in-place.