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POEXTENDS challenge: preprocessor function macros and class-like oop
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copied!<p><strong>Background</strong></p> <p>I've been using the C preprocessor to manage and "compile" semi-large javascript projects with multiple files and build targets. This gives full access to C preprocessor directives like <code>#include</code>, <code>#define</code>, <code>#ifdef</code>, etc. from within javascript. Here's a sample build script so you can test the example code:</p> <pre><code>#!/bin/bash export OPTS="-DDEBUG_MODE=1 -Isrc" for FILE in `find src/ | egrep '\.js?$'` do echo "Processing $FILE" cat $FILE \ | sed 's/^\s*\/\/#/#/' \ | cpp $OPTS \ | sed 's/^[#:<].*// ; /^$/d' \ > build/`basename $FILE`; done </code></pre> <p>Make a <code>src</code> and a <code>build</code> directory, and put the .js files in <code>src</code>.</p> <hr> <p><strong>Convenience Macros</strong></p> <p>Originally, I just wanted the preprocessor stuff for <code>#include</code> and maybe a few <code>#ifdef</code>s, but I got to thinking, wouldn't it be nice to have some convenience macros too? Experimentation ensued.</p> <pre><code>#define EACH(o,k) for (var k in o) if (o.hasOwnProperty(k)) </code></pre> <p>Cool, so now I can write something like this:</p> <pre><code>EACH (location, prop) { console.log(prop + " : " location[prop]); } </code></pre> <p>And it will expand to:</p> <pre><code>for (var prop in location) if (location.hasOwnProperty(prop)) { console.log(prop + " : " location[prop]); } </code></pre> <p>How about foreach?</p> <pre><code>#define FOREACH(o,k,v) var k,v; for(k in o) if (v=o[k], o.hasOwnProperty(k)) // ... FOREACH (location, prop, val) { console.log(prop + " : " + val) } </code></pre> <p>Notice how we sneak <code>v=o[k]</code> inside the <code>if</code> condition so it doesn't disturb the curly braces that should follow the invocation of this macro.</p> <hr> <p><strong>Class-like OOP</strong></p> <p>Let's start with a NAMESPACE macro and an obscure but useful js pattern...</p> <pre><code>#define NAMESPACE(ns) var ns = this.ns = new function() </code></pre> <p><code>new function(){ ... }</code> does some neat stuff. It calls an anonymous function as a constructor, so it doesn't need an extra <code>()</code> at the end to call it, and within it <code>this</code> refers to the object being created by the constructor, in other words, the namespace itself. This also allows us to nest namespaces within namespaces.</p> <p>Here is my full set of class-like OOP macros:</p> <pre><code>#define NAMESPACE(ns) var ns=this.ns=new function() #define CLASS(c) var c=this;new function() #define CTOR(c) (c=c.c=this.constructor=$$ctor).prototype=this;\ function $$ctor #define PUBLIC(fn) this.fn=fn;function fn #define PRIVATE(fn) function fn #define STATIC(fn) $$ctor.fn=fn;function fn </code></pre> <p>As you can see, these macros define many things both in the <code>Variable Object</code> (for convenience) and in <code>this</code> (from necessity). Here's some example code:</p> <pre><code>NAMESPACE (Store) { CLASS (Cashier) { var nextId = 1000; this.fullName = "floater"; CTOR (Cashier) (fullName) { if (fullName) this.fullName = fullName; this.id = ++nextId; this.transactions = 0; } PUBLIC (sell) (item, customer) { this.transactions += 1; customer.inventory.push(item); } STATIC (hire) (count) { var newCashiers = []; for (var i=count; i--;) { newCashiers.push(new Cashier()); } return newCashiers; } } CLASS (Customer) { CTOR (Customer) (name) { this.name = name; this.inventory = []; this.transactions = 0; } PUBLIC (buy) (item, cashier) { cashier.sell(this, item); } } } </code></pre> <hr> <p><strong>What about EXTENDS?</strong></p> <p>So this brings me to the question... how can we implement EXTENDS as a macro to wrap the usual "clone the prototype, copy constructor properties" js prototype inheritance? I haven't found a way to do it outside of requiring the EXTENDS to appear <em>after</em> the class definition, which is silly. This experiment needs EXTENDS or it's useless. Feel free to change the other macros as long as they give the same results.</p> <p>Edit - These might come in handy for EXTENDS; listing them here for completeness.</p> <pre><code>#define EACH(o,k) for(var k in o)if(o.hasOwnProperty(k)) #define MERGE(d,s) EACH(s,$$i)d[$$i]=s[$$i] #define CLONE(o) (function(){$$C.prototype=o;return new $$C;function $$C(){}}()) </code></pre> <p>Thanks in advance for any help, advice, or lively discussion. :)</p>

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