Question

I’d like to test if an id was not yet known or, if it is known, if the associated value has changed. I’m currently using code similar to this, but it is hard to understand for those not familiar with the pattern. Can you think of a way to make it more readable while keeping it short in LOC?

string id;
string actual;
string stored;

if (!someDictionary.TryGetValue (id, out stored) || stored != actual) {
    // id not known yet or associated value changed.
}

Answer 1

It looks fine to me…reads as easy as any other 2 condition if statement. About the only thing I’d possibly change is to flip the negations for an early exit:

if (someDictionary.TryGetValue(id, out stored) && stored == actual) {
    return;
}
// store new value

I don’t see any confusion in it at all, have never thought of it as a particularly troublesome idiom, and humbly suggest that those C# devs confused by it get used to it. It’s common, succint, and gives as many LOC to the problem as it deserves. Turning it into 10 lines of code makes it way too important.

If I used it often, an extension method named something like ContainsEqualValue would be appropriate – but I’d use the exact same code in the extension method as you have.