Type of conditional expression cannot be determined because there is no implicit conversion between 'lambda expression' and 'lambda expression'

Question

I've a collection of notes. Depending on the UI requesting those notes, I'd like to exclude some categories. This is just an example. If the project Notes popup requests notes, I should exclude collection notes.

Func<Note, bool> excludeCollectionCategory = (ui == UIRequestor.ProjectNotes) 
            ? x => x.NoteCategory != "Collections"
            : x => true; //-- error: cannot convert lambda to lambda

I'm getting the following error: Type of conditional expression cannot be determined because there is no implicit conversion between 'lambda expression' and 'lambda expression'

Thanks for helping

Answer 1

The compiler doesn't infer delegate types for lambda expressions. You need to specify the delegate type using a cast in the first ternary clause:

var excludeCollectionCategory = (ui == UIRequestor.ProjectNotes) 
    ? (Func<Note, bool>)(x => x.NoteCategory != "Collections")
    : x => true;

The silver lining is that you can use var instead of having to specify the type for the variable, so it isn't that much more verbose.