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<h1>Using methodMissing &amp; propertyMissing</h1>

<p>Since 1.5, Groovy supports the concept of &quot;methodMissing&quot;. This differs from <a class="confluence-link unresolved" data-content-title="Using invokeMethod &amp; getProperty" data-linked-resource-default-alias="Using invokeMethod &amp;amp; getProperty" href="#">invokeMethod</a> in that it is only invoked in the case of failed method dispatch.</p>

<p>There are a couple of important aspects to this behaviour:</p>
<ol>
	<li>Since method/propertyMissing only occur in the case of failed dispatch, they are expensive to execute</li>
	<li>Since method/propertyMissing aren't intercepting EVERY method call like <a class="confluence-link unresolved" data-content-title="Using invokeMethod &amp; getProperty" data-linked-resource-default-alias="Using invokeMethod &amp;amp; getProperty" href="#">invokeMethod</a> they can be more efficient with a few meta-programming tricks</li>
</ol>

<h2>Using methodMissing with dynamic method registration</h2>

<p>Typically when using methodMissing the code will react in some way that makes it possible for the next time the same method is called, that it goes through the regular Groovy method dispatch logic.</p>

<p>For example consider <a href="http://grails.org/GORM+-+Querying">dynamic finders</a> in GORM. These are implemented in terms of methodMissing. How does it work? The code resembles something like this:</p>
<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
class GORM {

def dynamicMethods = [...] // an array of dynamic methods that use regex
   def methodMissing(String name, args) {
       def method = dynamicMethods.find { it.match(name) }
       if(method) {
          GORM.metaClass."$name" = { Object[] varArgs ->
             method.invoke(delegate, name, varArgs)
          }
          return method.invoke(delegate,name, args)
       }
       else throw new MissingMethodException(name, delegate, args)
   }
}
</pre></td></tr></table>
<p>Notice how, if we find a method to invoke then we dynamically register a new method on the fly using <a class="confluence-link" href="/display/GROOVY/ExpandoMetaClass" data-linked-resource-id="79517" data-linked-resource-type="page" data-linked-resource-default-alias="ExpandoMetaClass" data-base-url="http://docs.codehaus.org">ExpandoMetaClass</a>. This is so that the next time the same method is called it is more efficient. This way methodMissing doesn't have the overhead of invokeMethod AND is not expensive for the second call</p>

<h2>Using propertyMissing</h2>

<p>Groovy also supports propertyMissing for dealing with property resolution attempts. For a getter you use a propertyMissing definition that takes a String argument:</p>
<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
class Foo {
   def propertyMissing(String name) { name }
}
def f = new Foo()

assertEquals "boo", f.boo
</pre></td></tr></table>
<p>For a setters you add a second propertyMissing definition that takes a value argument:</p>
<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
class Foo {
   def storage = [:]
   def propertyMissing(String name, value) { storage[name] = value }
   def propertyMissing(String name) { storage[name] }
}
def f = new Foo()
f.foo = "bar"

assertEquals "bar", f.foo
</pre></td></tr></table>
<p>As with methodMissing you will likely want to dynamically register new properties at runtime to improve the performance of you code.</p>

<h2>Static methods and properties</h2>

<p>You can add methodMissing and propertyMissing that deals with static methods and properties via <a class="confluence-link" href="/display/GROOVY/ExpandoMetaClass" data-linked-resource-id="79517" data-linked-resource-type="page" data-linked-resource-default-alias="ExpandoMetaClass" data-base-url="http://docs.codehaus.org">ExpandoMetaClass</a></p>