Interfaces and Structs

Interfaces

Interfaces are namespace-scope types that declare public instance method signatures.

public interface IReadable {
    int Read();
}

Current Phase 2/3 rules:

• interface members are method signatures only
• interfaces may inherit from other interfaces
• classes may implement multiple interfaces
• structs may implement interfaces
• no fields, constructors, statics, or default implementations yet

Structs

Structs are namespace-scope value types in the current bootstrap.

public struct TextSpan {
    private int start;
    private int length;

    public TextSpan(int s, int l) {
        start = s;
        length = l;
    }
}

Structs may contain:

• fields
• constructors
• instance methods
• static methods

Current semantics:

• struct locals and fields are zero-initialized by default
• assignment copies the value
• parameters and returns use copy semantics
• structs may implement interfaces
• converting a struct to an interface boxes a copy

Example

public interface ISpanView {
    int Start();
    int Length();
}

public struct TextSpan : ISpanView {
    private int start;
    private int length;

    public TextSpan(int s, int l) {
        start = s;
        length = l;
    }

    public int Start() {
        return start;
    }

    public int Length() {
        return length;
    }
}