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diff --git a/.html/java/kwargs.html b/.html/java/kwargs.html deleted file mode 100644 index 64cc16b..0000000 --- a/.html/java/kwargs.html +++ /dev/null @@ -1,223 +0,0 @@ -<!DOCTYPE html> -<html> -<head> - <title> - The Codex » - Keyword Arguments in Java - </title> - - <link - rel='stylesheet' - type='text/css' - href='http://fonts.googleapis.com/css?family=Buenard:400,700&subset=latin,latin-ext'> - <link - rel="stylesheet" - type="text/css" - href="../media/css/reset.css"> - <link - rel="stylesheet" - type="text/css" - href="../media/css/grimoire.css"> -</head> -<body> - -<div id="shell"> - - <ol id="breadcrumbs"> - - <li class="crumb-0 not-last"> - - <a href="../">index</a> - - </li> - - <li class="crumb-1 not-last"> - - <a href="./">java</a> - - </li> - - <li class="crumb-2 last"> - - kwargs - - </li> - - </ol> - - - - <div id="article"> - <h1 id="keyword-arguments-in-java">Keyword Arguments in Java</h1> -<h2 id="what">What</h2> -<p>Java arguments are traditionally passed by position:</p> -<pre><code>void foo(int x, int y, int z) -</code></pre> -<p>matches the call</p> -<pre><code>foo(1, 2, 3) -</code></pre> -<p>and assigns <code>1</code> to <code>x</code>, <code>2</code> to <code>y</code>, and <code>3</code> to <code>z</code> in the resulting -activation. Keyword arguments assign values to formal parameters by matching -the parameter's name, instead.</p> -<h2 id="why">Why</h2> -<p>Fuck the builder pattern, okay? Patterns like</p> -<pre><code>Response r = Response - .status(200) - .entity(foo) - .header("X-Plane", "Amazing") - .build(); -</code></pre> -<p>(from JAX-RS) mean the creation and maintenance of an entire separate type -just to handle arbitrary ordering and presence/absence of options. Ordering -can be done using keywords; presence/absence can be done by providing one -method for each legal combination of arguments (or by adding optional -arguments to Java).</p> -<p>The keyword-argument version would be something like</p> -<pre><code>Response r = new Response( - .status = 200, - .entity = foo, - .headers = Arrays.asList(Header.of("X-Plane", "Amazing")) -); -</code></pre> -<p>and the <code>ResponseBuilder</code> class would not need to exist at all for this case. -(There are others in JAX-RS that would still make <code>ResponseBuilder</code> mandatory, -but the use case for it gets much smaller.)</p> -<p>As an added bonus, the necessary class metadata to make this work would also -allow reflective frameworks such as Spring to make sensible use of the -parameter names:</p> -<pre><code><bean class="com.example.Person"> - <constructor-arg name="name" value="Erica McKenzie" /> -</bean> -</code></pre> -<h2 id="other-languages">Other Languages</h2> -<p>Python, most recently:</p> -<pre><code>def foo(x, y, z): - pass - -foo(z=3, x=1, y=2) -</code></pre> -<p>Smalltalk (and ObjectiveC) use an interleaving convention that reads very much -like keyword arguments:</p> -<pre><code>Point atX: 5 atY: 8 -</code></pre> -<h2 id="challenges">Challenges</h2> -<ul> -<li>Minimize changes to syntax.<ul> -<li>Make keyword arguments unambiguous.</li> -</ul> -</li> -<li>Minimize changes to bytecode spec.</li> -</ul> -<h2 id="proposal">Proposal</h2> -<p>Given a method definition</p> -<pre><code>void foo(int x, int y, int z) -</code></pre> -<p>Allow calls written as</p> -<pre><code>foo( - SOME-SYNTAX(x, EXPR), - SOME-SYNTAX(y, EXPR), - SOME-SYNTAX(z, EXPR) -) -</code></pre> -<p><code>SOME-SYNTAX</code> is a production that is not already legal at that point in Java, -which is a surprisingly frustrating limitation. Constructs like</p> -<pre><code>foo(x = EXPR, y = EXPR, z = EXPR) -</code></pre> -<p>are already legal (assignment is an expression) and already match positional -arguments.</p> -<p>Keyword arguments match the name of the formal argument in the method -declaration. Passing a keyword argument that does not match a formal argument -is a compilation error.</p> -<p>Calls can mix keyword arguments and positional arguments, in the following -order:</p> -<ol> -<li>Positional arguments.</li> -<li>Varargs positional arguments.</li> -<li>Keyword arguments.</li> -</ol> -<p>Passing the same argument as both a positional and a keyword argument is a -compilation error.</p> -<p>Call sites must satisfy every argument the method/constructor has (i.e., this -doesn't imply optional arguments). This makes implementation easy and -unintrusive: the compiler can implement keyword arguments by transforming them -into positional arguments. Reflective calls (<code>Method.invoke</code> and friends) can -continue accepting arguments as a sequence.</p> -<p>The <code>Method</code> class would expose a new method:</p> -<pre><code>public List<String> getArgumentNames() -</code></pre> -<p>The indexes in <code>getArgumentNames</code> match the indexes in <code>getArgumentTypes</code> and -related methods.</p> -<p>Possibilities for syntax:</p> -<ul> -<li> -<p><code>foo(x := 5, y := 8, z := 2)</code> - <code>:=</code> is never a legal sequence of tokens in - Java. Introduces one new operator-like construct; the new sequence <code>:=</code> - “looks like” assignment, which is a useful mnemonic.</p> -</li> -<li> -<p><code>foo(x ~ 5, y ~ 8, z ~ 2)</code> - <code>~</code> is not a binary operator and this is never - legal right now. This avoids introducing new operators, but adds a novel - interpretation to an existing unary operator that's not related to its - normal use.</p> -</li> -<li> -<p><code>foo(.x = 5, .y = 8, .z = 2)</code> - using <code>=</code> as the keyword binding feels more - natural. Parameter names must be legal identifiers, which means the leading - dot is unambiguous. This syntax is not legal anywhere right now (the dot - always has a leading expression). The dot is a “namespace” symbol already.</p> -</li> -</ul> -<p>To support this, the class file format will need to record the names of -parameters, not just their order. This is a breaking change, and generated -names will need to be chosen for existing class files. (This may be derivable -from debug information, where present.)</p> -<h2 id="edge-cases">Edge Cases</h2> -<ul> -<li>Mixed positional and keyword arguments.<ul> -<li>Collisions (same argument passed by both) are, I think, detectable at - compile time. This should be an error.</li> -</ul> -</li> -<li>Inheritance. It is legal for a superclass to define <code>foo(a, b)</code> and for - subclasses to override it as <code>foo(x, y)</code>. Which argument names do you use - when?</li> -<li>Varargs.</li> -</ul> - </div> - - - -<div id="comments"> -<div id="disqus_thread"></div> -<script type="text/javascript"> - /* * * CONFIGURATION VARIABLES: EDIT BEFORE PASTING INTO YOUR WEBPAGE * * */ - var disqus_shortname = 'grimoire'; // required: replace example with your forum shortname - - /* * * DON'T EDIT BELOW THIS LINE * * */ - (function() { - var dsq = document.createElement('script'); dsq.type = 'text/javascript'; dsq.async = true; - dsq.src = 'http://' + disqus_shortname + '.disqus.com/embed.js'; - (document.getElementsByTagName('head')[0] || document.getElementsByTagName('body')[0]).appendChild(dsq); - })(); -</script> -<noscript>Please enable JavaScript to view the <a href="http://disqus.com/?ref_noscript">comments powered by Disqus.</a></noscript> -<a href="http://disqus.com" class="dsq-brlink">comments powered by <span class="logo-disqus">Disqus</span></a> -</div> - - - - <div id="footer"> - <p> - - The Codex — - - Powered by <a href="http://markdoc.org/">Markdoc</a>. - -<a href="https://bitbucket.org/ojacobson/grimoire.ca/src/master/wiki/java/kwargs.md">See this page on Bitbucket</a> (<a href="https://bitbucket.org/ojacobson/grimoire.ca/history-node/master/wiki/java/kwargs.md">history</a>). - - </p> - </div> - -</div> -</body> -</html>
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