Question

Not often but sometimes I need to use String.Trim() to remove whitespaces of a string.
If it was a longer time since last trim coding I write:

string s = " text ";
s.Trim();

and be surprised why s is not changed. I need to write:

string s = " text ";
s = s.Trim();

Why are some string methods designed in this (not very intuitive) way? Is there something special with strings?

Answer 1

s.Trim() creates a new trimmed version of the original string and returns it instead of storing the new version in s. So, what you have to do is to store the trimmed instance in your variable:

  s = s.Trim();

This pattern is followed in all the string methods and extension methods.

The fact that string is immutable doesn’t have to do with the decision to use this pattern, but with the fact of how strings are kept in memory. This methods could have been designed to create the new modified string instance in memory and point the variable to the new instance.

It’s also good to remember that if you need to make lots of modifications to a string, it’s much better to use an StringBuilder, which behaves like a “mutable” string, and it’s much more eficient doing this kind of operations.