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Advanced Programming Techniques in D

union Examples

Explore how to implement unions and discriminated unions in D to handle data with varying types safely and efficiently. Understand how these constructs help represent protocol packets, provide type safety, and enable versatile collections through examples and D language features.

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Communication protocol

In some protocols like TCP/IP, the meanings of certain parts of a protocol packet depend on a specific value inside the same packet. Usually, it is a field in the header of the packet that determines the meanings of successive bytes. Unions can be used for representing such protocol packets.

The following design represents a protocol packet that has two kinds:

D
struct Host {

    // ...

}



struct ProtocolA {

    // ...

}



struct ProtocolB {

    // ...

}



enum ProtocolType { A, B }



struct NetworkPacket {

    Host source;

    Host destination;

    ProtocolType type;

    

    union {

        ProtocolA aParts;

        ProtocolB bParts;

    }

    

    ubyte[] payload;

}



void main() {}

The struct ...