<p>The <ahref="dynamic_extensions.html">dynamic extensions</a> is a easy way to extend the system. To enable fast lookups into route data, we can compile them into any shape (records, functions etc.) we want, enabling fast access at request-time.</p>
<p>Still, we can do much better. As we know the exact route that middleware/interceptor is linked to, we can pass the (compiled) route information into the middleware/interceptor at creation-time. It can do local reasoning: extract and transform relevant data just for it and pass it into the actual request-handler via a closure - yielding much faster runtime processing. It can also decide not to mount itself by returning <code>nil</code>. Why mount a <code>wrap-enforce-roles</code> middleware for a route if there are no roles required for it?</p>
<p>To enable this we use <ahref="data_driven_middleware.html">middleware records</a><code>:gen-wrap</code> key instead of the normal <code>:wrap</code>. <code>:gen-wrap</code> expects a function of <code>route-meta router-opts => ?wrap</code>.</p>
<p>To demonstrate the two approaches, below are response coercion middleware written as normal ring middleware function and as middleware record with <code>:gen-wrap</code>. Actual codes can be found in <ahref="https://github.com/metosin/reitit/blob/master/src/reitit/ring/coercion.cljc"target="_blank"><code>reitit.ring.coercion</code></a>:</p>
match (<spanclass="hljs-name">ring/get-match</span> request)
responses (<spanclass="hljs-name"><spanclass="hljs-builtin-name">-></span></span> match <spanclass="hljs-symbol">:result</span> method <spanclass="hljs-symbol">:meta</span><spanclass="hljs-symbol">:responses</span>)
coercion (<spanclass="hljs-name"><spanclass="hljs-builtin-name">-></span></span> match <spanclass="hljs-symbol">:meta</span><spanclass="hljs-symbol">:coercion</span>)
opts (<spanclass="hljs-name"><spanclass="hljs-builtin-name">-></span></span> match <spanclass="hljs-symbol">:meta</span><spanclass="hljs-symbol">:opts</span>)]
match (<spanclass="hljs-name">ring/get-match</span> request)
responses (<spanclass="hljs-name"><spanclass="hljs-builtin-name">-></span></span> match <spanclass="hljs-symbol">:result</span> method <spanclass="hljs-symbol">:meta</span><spanclass="hljs-symbol">:responses</span>)
coercion (<spanclass="hljs-name"><spanclass="hljs-builtin-name">-></span></span> match <spanclass="hljs-symbol">:meta</span><spanclass="hljs-symbol">:coercion</span>)
opts (<spanclass="hljs-name"><spanclass="hljs-builtin-name">-></span></span> match <spanclass="hljs-symbol">:meta</span><spanclass="hljs-symbol">:opts</span>)]
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