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Documentation on dynamic types (WIP) 

llvm-svn: 138425
This commit is contained in:
Enrico Granata 2011-08-24 04:53:31 +00:00
parent 03a8f9e578
commit c5df00f0b9
1 changed files with 47 additions and 3 deletions
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@ -1068,7 +1068,6 @@ Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.<br/>
<div class="post">
<h1 class="postheader">Filters</h1>
<div class="postcontent">
<p>Filters are a solution to the display of complex classes.
At times, classes have many member variables but not all of these are actually
necessary for the user to see.</p>
@ -1082,7 +1081,7 @@ Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.<br/>
<td class="content">
<b>(lldb)</b> type filter add Foo --child B --child H --child Q
</td>
<table>
</table>
<code> <b>(lldb)</b> frame variable a_foobar<br/>
(Foobar) a_foobar = {<br/>
&nbsp;&nbsp;&nbsp;&nbsp;(int) B = 1<br/>
@ -1090,7 +1089,52 @@ Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.<br/>
&nbsp;&nbsp;&nbsp;&nbsp;(std::string) Q = "Hello world"<br/>
}<br/>
</code> </p>
</div>
</div>
<div class="post">
<h1 class="postheader">Objective-C dynamic type discovery</h1>
<div class="postcontent">
<p>When doing Objective-C development, you may notice that some of your variables
come out as of type <code>id</code>. While this does not influence the ability
of the runtime to send messages to them, it can make it impossible for LLDB
to determine the actual formatters for that object.</p>
<p>The debugger, however, can dynamically discover the type of an Objective-C
variable, much like the runtime itself does when invoking a selector. In order
to let LLDB do that, however, a special option to <code>frame variable</code> is
required: <code>--dynamic-type</code>.</p>
<p><code>--dynamic-type</code> can have one of three values:
<ul>
<li><code>no-dynamic-values</code>: the default, prevents dynamic type discovery</li>
<li><code>no-run-target</code>: enables dynamic type discovery as long as running
code on the target is not required</li>
<li><code>run-target</code>: enables code execution on the target in order to perform
dynamic type discovery</li>
</ul>
</p>
<p>
If you specify a value of either <code>no-run-target</code> or <code>run-target</code>,
LLDB will detect the dynamic type of your variables and show the appropriate formatters
for them. As an example:
</p>
<p><table class="stats" width="620" cellspacing="0">
<td class="content">
<b>(lldb)</b> frame variable ns_string --dynamic-type no-run-target --show-types
</td>
</table>
<code>(id, dynamic type: __NSCFString) ns_string = 0x00000001001183d0 @&quot;An NSString saying hello world&quot;<br/>
</code>
<p>
Because LLDB uses a detection algorithm that does not need to invoke any functions
on the target process, <code>no-run-target</code> is enough for this to work.
As a final sidenote on this, LLDB is currently able to provide a summary string for <code>NSString</code>
that shows the content of the string, without requiring you to run code on the target
process. <a href="http://llvm.org/svn/llvm-project/lldb/trunk/examples/synthetic/CFString.py">
CFString.py</a> contains the code for such a Python summary provider (the code is well commented,
but you may find it hard to follow if it is your first time dealing with LLDB formatting features)
and <a href="http://llvm.org/svn/llvm-project/lldb/trunk/test/functionalities/data-formatter/data-formatter-objc/">
this test case</a> contains an usage example.
</p>
</div>
</div>