Question

I have always been taught that programming against an interface is better, so parameters on my methods I would set to IList<T> rather than List<T>..

But this means I have to cast to List<T> just to use some methods, one comes to mind is Find for example.

Why is this? Should I continue to program against interfaces, but continue to cast or revert?

I am a little bit confused why Find (for example) isn’t available on the IList<T> which List<T> inherits from.

Answer 1

Personally I would use IList<T> rather than List<T>, but then use LINQ (Select, Where etc) instead of the List-specific methods.

Casting to List<T> removes much of the point of using IList<T> in the first place – and actually makes it more dangerous, as the implementation may be something other than List<T> at execution time.