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Copy file name to clipboardExpand all lines: clojure+/print/objects_and_protocols.html
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@@ -395,20 +395,20 @@ <h1 class="title">Printing Objects and Protocols in Clojure</h1>
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<spanid="cb1-2"><ahref="#cb1-2" aria-hidden="true" tabindex="-1"></a> (<spanclass="va">#'clojure.core/print-object</span> x w))</span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
<p>The syntax is <code>#object[CLASS-NAME HASH toString())]</code> and as you can see, the toString of an Object is <code>CLASS-NAME@HASH</code>. This can get pretty ugly:</p>
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<divclass="sourceCode" id="cb5"><preclass="sourceCode clojure code-with-copy"><codeclass="sourceCode clojure"><spanid="cb5-1"><ahref="#cb5-1" aria-hidden="true" tabindex="-1"></a>(async/chan)</span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
<p><ahref="https://github.com/tonsky/clojure-plus">clojure-plus</a> provides print-methods to improve printing many things.</p>
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<spanid="cb14-3"><ahref="#cb14-3" aria-hidden="true" tabindex="-1"></a> (.getName))</span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
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<divclass="sourceCode" id="cb15"><preclass="sourceCode clojure code-with-copy"><codeclass="sourceCode clojure"><spanid="cb15-1"><ahref="#cb15-1" aria-hidden="true" tabindex="-1"></a><spanclass="st">"clojure_PLUS_.print.objects_and_protocols$eval72596$_PERCENT__PERCENT___72597$_PERCENT__PERCENT__PERCENT___72598"</span></span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
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<divclass="sourceCode" id="cb15"><preclass="sourceCode clojure code-with-copy"><codeclass="sourceCode clojure"><spanid="cb15-1"><ahref="#cb15-1" aria-hidden="true" tabindex="-1"></a><spanclass="st">"clojure_PLUS_.print.objects_and_protocols$eval72683$_PERCENT__PERCENT___72684$_PERCENT__PERCENT__PERCENT___72685"</span></span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
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<p>Whoa, that’s pretty gross. We’d prefer to demunge the names at least.</p>
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<spanid="cb17-2"><ahref="#cb17-2" aria-hidden="true" tabindex="-1"></a> (class-name))</span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
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<divclass="sourceCode" id="cb18"><preclass="sourceCode clojure code-with-copy"><codeclass="sourceCode clojure"><spanid="cb18-1"><ahref="#cb18-1" aria-hidden="true" tabindex="-1"></a><spanclass="st">"clojure+.print.objects-and-protocols/eval72603/%%--72604/%%%--72605"</span></span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
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<divclass="sourceCode" id="cb18"><preclass="sourceCode clojure code-with-copy"><codeclass="sourceCode clojure"><spanid="cb18-1"><ahref="#cb18-1" aria-hidden="true" tabindex="-1"></a><spanclass="st">"clojure+.print.objects-and-protocols/eval72690/%%--72691/%%%--72692"</span></span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
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<p>Notice the <code>/evalNNNNN/</code> part? To create a function, Clojure creates a new class. The <code>/evalNNNNN/</code> counts every time it evaluates. This is useful in the sense that it identifies the class for that evaluation. But we almost never care for that detail (more on that later). For the same reason our strangely named functions have <code>--NNNNN</code> appended to them, because they are sub evaluations of the top-level evaluation.</p>
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<p>Let’s do away with that noise for the moment:</p>
<spanid="cb1-2"><ahref="#cb1-2" aria-hidden="true" tabindex="-1"></a> (<spanclass="va">#'clojure.core/print-object</span> x w))</span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
<p>The syntax is <code>#object[CLASS-NAME HASH toString())]</code> and as you can see, the toString of an Object is <code>CLASS-NAME@HASH</code>. For most objects this becomes quite a long string.</p>
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<divclass="sourceCode" id="cb5"><preclass="sourceCode clojure code-with-copy"><codeclass="sourceCode clojure"><spanid="cb5-1"><ahref="#cb5-1" aria-hidden="true" tabindex="-1"></a>(async/chan)</span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
<p>It’s quite easy to miss the fact that it is a function as we are looking for a tiny little <code>fn</code> in a sea of text. If, like me, you are fond of the <ahref="../../code_interview/beating/with_stupid_stuff/z_combinator_gambit.html">odd lambda calculus excursion</a>, things get even more hectic.</p>
<p>Yikes! what an eyesore. This is not an academic issue specific to lambda calculus. Any function created from inside a function is helpfully identifiable through the <code>fn$fn</code> nesting. We create these quite regularly, and they are often printed in stack traces. I’m sure you have seen them when you map an inline function across a seq, and there is a bug in the anonymous function.</p>
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