Question

what is the memory overhead on the stack and heap of A versus B

A:

private string TestA() {      string a = _builder.Build();      return a;        } 

B:

private string TestB() {      return _builder.Build(); } 

Answer 1

re the efficiency question; the two are identical, and in release mode will be reduced to the same thing. Either way, string is a reference-type, so the string itself is always on the heap. The only thing on the stack would be the reference to the string – a few bytes (no matter the string length).

‘do all local variables go on the stack’: no; there are two exceptions:

• captured variables (anonymous methods / lambdas)
• iterator blocks (yield return etc)

In both cases, there is a compiler generated class behind the scenes:

int i = 1; Action action = delegate {i++;}; action(); Console.WriteLine(i); 

is similar to:

class Foo {     public int i; // yes, a public field     public void SomeMethod() {i++;} } ... Foo foo = new Foo(); foo.i = 1; Action action = foo.SomeMethod; action(); Console.WriteLine(foo.i); 

Hence i is on an object, hence on the heap.

Iterator blocks work in a similar way, but with the state machine.