Tuple equality for Dictionary

Question

I need a compound key (two strings) as my lookup value for a dictionary. I was thinking I could use a Tuple<string,string> for this, but as I understand it, the dictionary would perform a reference equality check, and I'd never get a match.

What can I do so that it will perform an actual string comparison?

Here's what I've got:

protected Dictionary<Tuple<string, string>, WopiSession> _sessions;

...

var sessionKey = new Tuple<string, string>(accessToken, fileToken);
WopiSession session;

if (!_sessions.TryGetValue(sessionKey, out session))
{
    session = new WopiSession();
    _sessions.Add(sessionKey, session);
}

@poke I'm going to....it's a complex program. It'll be another hour or so before I'm able to test it. I knew someone here would have the answer off the top of their head though, so why not ask before going down the wrong path? — mpen, Oct 10 '14 at 16:52
possible duplicate of [Tuples( or arrays ) as Dictionary keys in C#](http://stackoverflow.com/questions/955982/tuples-or-arrays-as-dictionary-keys-in-c-sharp) — poke, Oct 10 '14 at 16:53
also possible duplicate of [Composite Key Dictionary](http://stackoverflow.com/questions/2877660/composite-key-dictionary) — poke, Oct 10 '14 at 16:54
Yeah and so you didn't even bothered to search for a duplicate question here. — Rahul, Oct 10 '14 at 16:55
@Rahul If you must know I did perform a search on tuple equality which mentioned it performing reference equality, after which I assumed it wouldn't work with a dictionary. Didn't realize that only applied to `==` and not `.Equals`, which Dictionary uses. Anyway, if you've got a problem with this, close it as a dupe. — mpen, Oct 10 '14 at 17:39
@Rahul I'm not offended. That's what you're supposed to do if there's a dupe. What you're not supposed to do is berate me for overlooking it. — mpen, Oct 10 '14 at 17:53
`berate me for overlooking it` .. Oh! No .. don't get me wrong from my comment. That comment just meant to say .. "You mostly have didn't searched properly" and not to make you feel bad. No bad feelings .. Peace brother. — Rahul, Oct 11 '14 at 08:55

score 2 · Accepted Answer · answered Oct 10 '14 at 16:45

You don't need to do anything. Tuple override the default equality semantics of object to instead create a composite hash of the hashes of all of the objects it represents, and its Equals method compares each of the composed items for equality. Since strings also override equality based on the semantics of string equality, your code will work as is.

Tuple equality for Dictionary

1 Answers1