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copied!<p>From what you've described, <strong>Decorator</strong> is not the pattern to be looking at.</p> <p>It sounds to me like you simply want to set up a chain of transformers to operate upon a common vector – i.e. a simple <em>functional composition</em>. This differs from <strong>Decorator</strong> in terms of the relationship to the object at the core - you are not building something to <em>stand in</em> for a vector, you are building something to <em>operate upon</em> it. Now when you take multiple transformers, you could theoretically imagine the second and later transformers as <em>decorators</em> of the first, but given the simplicity of the objects involved, trying to apply the GoF decorator implementation to your situation is probably going to be overkill.</p> <p>You can KISS by doing something like this:</p> <pre><code>#include <vector> using namespace std; typedef vector<int> ivec; ivec& a(ivec& v) { v.push_back(1); return v; } ivec& b(ivec& v) { v.push_back(2); v.push_back(3); v.push_back(4); return v; } ivec& c(ivec& v) { v.pop_back(); return v; } </code></pre> <p>There are three simple transformation functions, each written so that the output of one can be fed right into the input of the next. Then you can do something like:</p> <pre><code>ivec& xform(ivec& v) { return c(b(a(v))); } ivec v; xform(v); </code></pre> <p>if you want to just build up your final transform statically and apply it.</p> <p>As an alternate implementation, let's say you wanted to build up a set of transformers <em>dynamically</em>. In that case, you can push the functions into a vector of transformers and apply them one by one:</p> <pre><code>#include <vector> using namespace std; typedef ivec& (*ivec_xformer)(ivec&); typedef vector<ivec_xformer> xform_vec; xform_vec xforms; xforms.add(&a); xforms.add(&b); xforms.add(&c); ivec v; for (xform_vec::iterator i = xforms.begin(); i != xforms.end(); ++i) { (*i)(v); } </code></pre> <p>This loop at the end, btw, can be further "simplified" with <code>boost::bind</code> and <code>std::for_each</code> if you're so inclined.</p> <p>The dynamic chain of transformers bears some resemblance to a <strong>Chain of Responsibility</strong>, except that there's no concept of having a particular object stop the chain by "handling" the request, i.e. there's no real <em>responsibility</em> associated with this solution – each function gets an equal crack at the vector. I'd suggest this pattern needs a better name – one probably already exists out there, as this kind of functional composition in OO programming is not uncommon, but it eludes me at the moment.</p>

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