What is the best way to copy a StringBuilder?

Question

What is the best way (performance wise) to instantiate a new StringBuilder from another one? (Copy-Ctor).

I don't want to pass via an immutable string as the underline data is very big.

so the below is valid, but not wanted.

StringBuilder newSB = new StringBuilder(oldSB.ToString());

I want something like

StringBuilder newSB = new StringBuilder(oldSB);

But this is not supported.

Answer 1

There’s an overload of Append for other StringBuilder instances:

var newSB = new StringBuilder(oldSB.Length);
newSB.Append(oldSB);