Can we use GetEnumerator() without using IEnumerable interface?

I have a class called Primes and this class implements GetEnumerator() without implementing IEnumerable interface.

public class Primes
{
    private long min;
    private long max;

    public Primes()
        : this(2, 100)
    {
    }

    public IEnumerator GetEnumera开发者_JS百科tor()
    {...}

I don't get it. Am I missing something?

Firstly, as others have said you can introduce your own methods without implementing interfaces anyway - you can write your own Dispose method without implementing IDisposable etc. For well-known interfaces I'd suggest this is almost a bad idea (as readers will have certain expectations) but it's entirely valid.

More importantly though, the foreach statement in C# can work without IEnumerable being involved. The compiler effectively does compile-time duck typing on the names GetEnumerator(), Current and MoveNext(). This was primarily to allow strongly-typed (and non-boxing) iteration in C# 1, before generics. See section 8.8.4 of the C# 3 spec for more details.

However, it's generally a bad idea to do this now if you do want to be able to easily iterate over the contents of an instance as a collection - and indeed I'd suggest implementing IEnumerable<T> instead of just IEnumerable.

yes you can. even you can use it in foreach. The only problem that objects of this class can't be cast to IEnumerable although they implement needed method.

There's no reason that you have to implement IEnumerable in order to create a function called GetEnumerator that returns an IEnumerator, that just means that you won't be able to supply an instance of that type to something that expects an IEnumerable.

an interface ensures a contract, that does not mean that you can't have a method with the same signature as one in the interface on a class that does not impliment the interface.