Check if return type is IEnumerable<T>

Question

How can I check if the return type of a function is IEnumerable<T>? In other words, I don't want to match List<T>, even though it implements IEnumerable<T>. Or put even another way, how can I detect if a function has deferred execution?

Answer 1

I assume you are interacting with a MethodInfo?

Type returnType = methodInfo.ReturnType;
bool isEnumerable = returnType.IsGenericType && 
                    returnType.GetGenericTypeDefinition() == typeof(IEnumerable<>);

Of course, just because it returns IEnumerable doesn't mean it uses deferred execution (i.e. yield return) and there's no real way to check for that without decompiling the code.