Question

Is this a good or bad idea?

public interface IRepository<T>
{
    ...
    IList<T> Get(Func<T, bool> predicate)
    ...
}

I mean – it seems really powerful addition and i could implement it too (at least – to some level) but my guts tells me it’s kind a wrong. Could anyone enlighten me?

Answer 1

Well, it certainly is a powerful feature. The problem is: introducing it in the interface will force all implementations of IRepository to provide a suitable definition — which might not be possible (or at least really hard) depending on the implementation (say, an implementation backed by a database connection or something).

Maybe, you should instead do

public interface IRepository<T>
{
    ...
}

public interface IAdvancedRepository<T>: IRepository<T> 
{
    IList<T> Get(Func<T, bool> predicate)
}

and provide Get only, if the implementation can do it efficiently.