CODEWITHSUNDEEP
c#
KDecker
KDecker

Reputation: 7128

Force subclasses to implement two interfaces

Lets say that I have a class that represents a Stream and that I subclass this class to add the methods read and write. These two methods are defined in two separate interfaces IWriteableStream and IReadableStream. 

public class MyFooStream : Stream, IWriteableStream, IReadableStream

How can I force the developer who subclasses from Stream to implement the interfaces so that I can enforce the idea that all Stream must be readable and writeable?

EDIT: So my solution has been to make Stream abstract and implement the two interfaces. Then the interfaces methods are marked as abstract in Stream forcing subclasses to implement them. 

public abstract class Stream : IWriteableStream, IReadableStream
{
    public abstract void WriteToStream();
    public abstract void ReadFromStream();
}

public class WaterStream : Stream
{
    public override void WriteToStream() {}
    public override void ReadFromStream() {}
}

Upvotes: 1

Views: 88

Answers (2)

James
James

Reputation: 82096

If the interface methods are implemented in the base class then any derivation of Stream will inherit these and as such already be implementing both IWritableStream / IReadableStream.

If you want to force them to override the default behaviour, then you could make read/write methods abstract (or the entire class if need be).

Example

public class MyFooStream : Stream, IWritableStream, IReadableStream
{
    public abstract void Write(byte[] data);
    public abstract byte[] Read();
}

// if I don't override Write/Read methods the compiler will complain
public class ReadableStream : MyFooStream
{
    public override void Write(byte[] data)
    {
        ...
    }

    public override byte[] Read()
    {
        ...
    }
}

Upvotes: 2

pete the pagan-gerbil
pete the pagan-gerbil

Reputation: 3166

Make MyFooStream an abstract class, and 'implement' those methods on the abstract class as abstract methods - all derived classes will have to have implementations for those methods.

Upvotes: 4

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