Question

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String vs StringBuilder

i know .NET Strings are immutable which is the reason why a new string object is created every time we alter it (insert, append, remove, etc.).

That sounds reasonable, so why do we still use the .NET String class functions and not the faster StringBuilder?

Answer 1

StringBuilder is faster for repeated (non-compile-time) concatenations in a loop.

For ordinary string operations, they perform equivalently.

In particular, a + b + c is compiled as String.Concat(a, b, c), which allocates a single buffer and is as fast or faster than a string builder.
StringBuilder is only faster than multiple separate Concats, since each Concat will need to make a new buffer.