Trying to modify Strings

[DNA]

Hello,

I'm trying to write code that does the following:

//someString = "ABC"
let mut newString = someString.insert(1,c);
// c = 'A'

So the end result would be: newString = AABC

However, for some reason, using insert changes newString from being a String and turns it into ().

Hopefully someone can help me understand what I'm missing? I've been using Rust for just a couple of weeks.

Many thanks

[leudz]

Hi, insert modifies the string in place that's why you have (), the documentation of the unit type explains it.
If your string is mutable you can simply do:

someString.insert(1, c);

and the string will be modified. If you don't want to modify someString and/or it's immutable you can do:

let mut newString = someString.clone();
newString.insert(1, c);

or more complicated but probably with better performance:

let mut newString = String::with_capacity(someString.capacity() + c.len_utf8());
newString.push_str(&someString[0..1]);
newString.push(c);
newString.push_str(&someString[1..]);

I can't think of a way to have a pretty and efficient version but I'm curious to see what other people will propose.

[matt1992]

insert modifies the String in-place, it doesn't return any useful value. If you print someString after calling insert you'll see that it was mutated.