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PODiamond inheritance (C++)
 

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    <p>I know that having diamond inheritance is considered bad practice. However, I have 2 cases in which I feel that diamond inheritance could fit very nicely. I want to ask, would you recommend me to use diamond inheritance in these cases, or is there another design that could be better.</p> <p><strong>Case 1:</strong> I want to create classes that represent different kinds of "Actions" in my system. The actions are classified by several parameters: </p> <ul> <li>The action can be "Read" or "Write".</li> <li>The action can be with delay or without delay (It is not just 1 parameter. It changes the behavior significantly).</li> <li>The action's "flow type" can be FlowA or FlowB.</li> </ul> <p>I intend to have the following design:</p> <pre><code>// abstract classes class Action { // methods relevant for all actions }; class ActionRead : public virtual Action { // methods related to reading }; class ActionWrite : public virtual Action { // methods related to writing }; class ActionWithDelay : public virtual Action { // methods related to delay definition and handling }; class ActionNoDelay : public virtual Action {/*...*/}; class ActionFlowA : public virtual Action {/*...*/}; class ActionFlowB : public virtual Action {/*...*/}; // concrete classes class ActionFlowAReadWithDelay : public ActionFlowA, public ActionRead, public ActionWithDelay { // implementation of the full flow of a read command with delay that does Flow A. }; class ActionFlowBReadWithDelay : public ActionFlowB, public ActionRead, public ActionWithDelay {/*...*/}; //... </code></pre> <p>Of course, I will obey that no 2 actions (inheriting from Action class) will implement the same method.</p> <p><strong>Case 2:</strong> I implement the composite design pattern for a "Command" in my system. A command can be read, written, deleted, etc. I also want to have a sequence of commands, which can also be read, written, deleted, etc. A sequence of commands can contain other sequences of commands. </p> <p>So I have the following design:</p> <pre><code>class CommandAbstraction { CommandAbstraction(){}; ~CommandAbstraction()=0; void Read()=0; void Write()=0; void Restore()=0; bool IsWritten() {/*implemented*/}; // and other implemented functions }; class OneCommand : public virtual CommandAbstraction { // implement Read, Write, Restore }; class CompositeCommand : public virtual CommandAbstraction { // implement Read, Write, Restore }; </code></pre> <p>In addition, I have a special kind of commands, "Modern" commands. Both one command and composite command can be modern. Being "Modern" adds a certain list of properties to one command and composite command (mostly same properties for both of them). I want to be able to hold a pointer to CommandAbstraction, and initialize it (via new) according to the needed type of command. So I want to do the following design (in addition to the above) :</p> <pre><code>class ModernCommand : public virtual CommandAbstraction { ~ModernCommand()=0; void SetModernPropertyA(){/*...*/} void ExecModernSomething(){/*...*/} void ModernSomethingElse()=0; }; class OneModernCommand : public OneCommand, public ModernCommand { void ModernSomethingElse() {/*...*/}; // ... few methods specific for OneModernCommand }; class CompositeModernCommand : public CompositeCommand, public ModernCommand { void ModernSomethingElse() {/*...*/}; // ... few methods specific for CompositeModernCommand }; </code></pre> <p>Again, I will make sure that no 2 classes inheriting from CommandAbstraction class will implement the same method.</p> <p>Thank you.</p>
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