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| <title>Using Variable-length arguments in advice and pointcut expressions</title><link rel="stylesheet" href="aspectj-docs.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.44"><link rel="home" href="index.html" title="The AspectJTM 5 Development Kit Developer's Notebook"><link rel="up" href="varargs.html" title="Chapter 6. Varargs"><link rel="previous" href="varargs.html" title="Chapter 6. Varargs"><link rel="next" href="enumeratedtypes.html" title="Chapter 7. Enumerated Types"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Using Variable-length arguments in advice and pointcut expressions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="varargs.html">Prev</a> </td><th width="60%" align="center">Chapter 6. Varargs</th><td width="20%" align="right"> <a accesskey="n" href="enumeratedtypes.html">Next</a></td></tr></table><hr></div><div class="sect1"><a name="varargs-in-pcds"></a><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="varargs-in-pcds"></a>Using Variable-length arguments in advice and pointcut expressions</h2></div></div><p>AspectJ 5 allows variable-length arguments to be used for methods declared within | |
| aspects, and for inter-type declared methods and constructors, in accordance with the rules | |
| outlined in the previous section.</p><p> | |
| AspectJ 5 also allows variable length arguments to be matched by pointcut expressions and | |
| bound as formals in advice. | |
| </p><div class="sect2"><a name="matching-signatures-based-on-variable-length-argument-types"></a><div class="titlepage"><div><h3 class="title"><a name="matching-signatures-based-on-variable-length-argument-types"></a>Matching signatures based on variable length argument types</h3></div></div><p> | |
| Recall from the definition of signature patterns given in the chapter on | |
| annotations (<a href="annotations-pointcuts-and-advice.html#signaturePatterns">Signature Patterns</a>), that <tt>MethodPattern</tt> | |
| and <tt>ConstructorPattern</tt> are extended to allow a <tt>varargs</tt> | |
| pattern in the last argument position of a method or constructor signature. | |
| </p><pre class="programlisting"> | |
| FormalsPattern := '..' (',' FormalsPatternAfterDotDot)? | | |
| OptionalParensTypePattern (',' FormalsPattern)* | | |
| TypePattern '...' | |
| FormalsPatternAfterDotDot := | |
| OptionalParensTypePattern (',' FormalsPatternAfterDotDot)* | | |
| TypePattern '...' | |
| </pre><p> | |
| Method and constructor patterns are used in the <tt>call</tt>, | |
| <tt>execution</tt>, <tt>initialization</tt>, | |
| <tt>preinitialization</tt>, and <tt>withincode</tt> | |
| pointcut designators. Some examples of usage follow: | |
| </p><div class="variablelist"><dl><dt><a name="d0e3347"></a><span class="term">call(* org.xyz.*.*(int, String...))</span></dt><dd><p><a name="d0e3350"></a> | |
| Matches a call join point for a call to a method defined in the | |
| <tt>org.xyz</tt> package, taking an <tt>int</tt> | |
| and a <tt>String vararg</tt>. | |
| </p></dd><dt><a name="d0e3362"></a><span class="term">execution(* org.xyz.*.*(Integer...))</span></dt><dd><p><a name="d0e3365"></a> | |
| Matches an execution join point for the execution of a method defined in the | |
| <tt>org.xyz</tt> package, taking an <tt>Integer vararg</tt>. | |
| </p></dd><dt><a name="d0e3374"></a><span class="term">initialization(org.xyz.*.new((Foo || Goo)...))</span></dt><dd><p><a name="d0e3377"></a> | |
| Matches the initialization join point for the construction of an | |
| object in the <tt>org.xyz</tt> package via a constructor | |
| taking either a variable number of <tt>Foo</tt> parameters or | |
| a variable number of <tt>Goo</tt> parameters. (This example | |
| illustrating the use of a type pattern with ...). | |
| </p></dd></dl></div><p>A variable argument parameter and an array parameter are treated as distinct | |
| signature elements, so given the method definitions: | |
| </p><pre class="programlisting"> | |
| void foo(String...); | |
| void bar(String[]); | |
| </pre><p> | |
| The pointcut <tt>execution(* *.*(String...))</tt> matches the execution join point | |
| for <tt>foo</tt>, but not <tt>bar</tt>. The pointcut | |
| <tt>execution(* *.*(String[]))</tt> matches the execution join point | |
| for <tt>bar</tt> but not <tt>foo</tt>. | |
| </p></div><div class="sect2"><a name="exposing-variable-length-arguments-as-context-in-pointcuts-and-advice"></a><div class="titlepage"><div><h3 class="title"><a name="exposing-variable-length-arguments-as-context-in-pointcuts-and-advice"></a>Exposing variable-length arguments as context in pointcuts and advice</h3></div></div><p> | |
| When a varargs parameter is used within the body of a method, it has | |
| an array type, as discussed in the introduction to this section. We follow the | |
| same convention when binding a varargs parameter via the <tt>args</tt> | |
| pointcut designator. Given a method | |
| </p><pre class="programlisting"> | |
| public void foo(int i, String... strings) { | |
| } | |
| </pre><p> | |
| The call or execution join points for <tt>foo</tt> will be matched | |
| by the pointcut <tt>args(int,String[])</tt>. It is not permitted | |
| to use the varargs syntax within an args pointcut designator - so you | |
| <span class="emphasis"><i>cannot</i></span> write <tt>args(int,String...)</tt>. | |
| </p><p> | |
| Binding of a varargs parameter in an advice statement is straightforward: | |
| </p><pre class="programlisting"> | |
| before(int i, String[] ss) : call(* foo(int,String...)) && args(i,ss) { | |
| // varargs String... argument is accessible in advice body through ss | |
| // ... | |
| } | |
| </pre><p>Since you cannot use the varargs syntax in the <tt>args</tt> | |
| pointcut designator, you also cannot use the varargs syntax to declare | |
| advice parameters.</p><p>Note: the proposal in this section does not allow you to | |
| distinguish between a join point with a signature (int, String...) | |
| and a join point with a signature (int, String[]) based | |
| <span class="emphasis"><i>solely</i></span> on the use of the <tt>args</tt> | |
| pointcut designator. If this distinction is required, <tt>args</tt> | |
| can always be coupled with <tt>call</tt> or | |
| <tt>execution</tt>.</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="varargs.html">Prev</a> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right"> <a accesskey="n" href="enumeratedtypes.html">Next</a></td></tr><tr><td width="40%" align="left">Chapter 6. Varargs </td><td width="20%" align="center"><a accesskey="u" href="varargs.html">Up</a></td><td width="40%" align="right"> Chapter 7. Enumerated Types</td></tr></table></div></body></html> |