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POTesting a c++ class for features
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  1. POTesting a c++ class for features
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    copied!<p>I have a set of classes that describe a set of logical boxes that can hold things and do things to them. I have</p> <pre><code>struct IBox // all boxes do these { .... } struct IBoxCanDoX // the power to do X { void x(); } struct IBoxCanDoY // the power to do Y { void y(); } </code></pre> <p>I wonder what is the 'best' or maybe its just 'favorite' idiom for a client of these classes to deal with these optional capabilities</p> <p>a)</p> <pre><code> if(typeid(box) == typeid(IBoxCanDoX)) { IBoxCanDoX *ix = static_cast&lt;IBoxCanDoX*&gt;(box); ix-&gt;x(); } </code></pre> <p>b)</p> <pre><code> IBoxCanDoX *ix = dynamic_cast&lt;IBoxCanDoX*&gt;(box); if(ix) { ix-&gt;x(); } </code></pre> <p>c) </p> <pre><code>if(box-&gt;canDoX()) { IBoxCanDoX *ix = static_cast&lt;IBoxCanDoX*&gt;(box); ix-&gt;x(); } </code></pre> <p>d) different class struct now</p> <pre><code>struct IBox { void x(); void y(); } ... box-&gt;x(); /// ignored by implementations that dont do x </code></pre> <p>e) same except </p> <pre><code>box-&gt;x() // 'not implemented' exception thrown </code></pre> <p>f) explicit test function</p> <pre><code>if(box-&gt;canDoX()) { box-&gt;x(); } </code></pre> <p>I am sure there are others too.</p> <p>EDIT:</p> <p>Just to make the use case clearer</p> <p>I am exposing this stuff to end users via interactive ui. They can type 'make box do X'. I need to know if box can do x. Or I need to disable the 'make current box do X' command</p> <p>EDIT2: Thx to all answerers</p> <p>as Noah Roberts pointed out (a) doesnt work (explains some of my issues !). I ended up doing (b) and a slight variant</p> <pre><code> template&lt;class T&gt; T* GetCurrentBox() { if (!current_box) throw "current box not set"; T* ret = dynamic_cast&lt;T*&gt;(current_box); if(!ret) throw "current box doesnt support requested operation"; return ret; } ... IBoxCanDoX *ix = GetCurrentBox&lt;IBoxCanDoX&gt;(); ix-&gt;x(); </code></pre> <p>and let the UI plumbing deal nicely with the exceptions (I am not really throwing naked strings). </p> <p>I also intend to explore Visitor</p>
 

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