Question

I have a List<KeyValuePair<string, othertype>>. I need to do something along the lines of

list.Find(x=>x.Key=="foobar")

However, if that doesn’t exist in the list, what will the behavior be? Usually it would return null, but structs can’t be null.

Answer 1

It will return the default(T) which will be the same as new KeyValuePair<string, othertype>>(), that is, a default initialized struct.

Basically, the default for reference types is always null, and for value types (including struct) it’s the default (0 for numerics, false for bool, a struct with every field defaulted for structures, etc.)

So, for a default(KeyValuePair<string, othertype>>) you’d get back a KVP where the Key was null (default for string) and whatever the default(othertype) would be (as in the examples above)…

From the MSDN:

The first element that matches the conditions defined by the specified
predicate, if found; otherwise, the default value for type T.

Using this, if you wanted to check and see if you got back the default, I’d recommend checking for yourResult.Key != null to see if you got a result, or you could use a different Find method such as FindIndex as Olivier suggests.