Strings Reference riddle

Question

I've encountered with the following code riddle:

string a = "S1";
string b = "S2";
a = a+b;

What will stay in the memory after this:

"S1S2", "S2"
"S1", "S1S2"
"S1", "S2", "S1S2"

What is your opinion? And why, in my opinion (c)

string a pointing to "S1S2"
string b pointing to "S2"
And "S1" is also in the background even after changing pointer/reference of string a

The first thing you get, is a compiler error for redeclaring `a`. — Moo-Juice, Dec 24 '13 at 20:50
Run it and find out. It took you more time to ask this question than it did to find the answer. — Servy, Dec 24 '13 at 20:52
Riddle? Sounds like something for [CodeReview](http://codereview.stackexchange.com/) or [CodeGolf](http://codegolf.stackexchange.com/). — Theraot, Dec 24 '13 at 20:52
@Theraot He's not asking to improve it, so CR is out, there's no problem to solve, so CG doesn't make sense. — Servy, Dec 24 '13 at 20:52
possible duplicate of [Strings vs classes when both are reference types](http://stackoverflow.com/questions/20739996/strings-vs-classes-when-both-are-reference-types) — Ondrej Janacek, Dec 24 '13 at 20:57
This question appears to be off-topic because it is not a real question. — Reinstate Monica -- notmaynard, Dec 24 '13 at 21:01

score 5 · Accepted Answer · edited Jun 20 '20 at 09:12

I think c is correct answer, but the reason does not match yours.

You have to be aware of intern pool:

The common language runtime automatically maintains a table, called the intern pool, which contains a single instance of each unique literal string constant declared in a program, as well as any unique instance of String you add programmatically by calling the Intern method.

String.IsInterned Method

And that's why both S1 and S2 will be within intern pool even if there is no reference to them.

And why S1S2 will be in memory is quite obvious - a points to that string.

Strings Reference riddle

1 Answers1