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[docs][LLVM-style RTTI] Add a mention of multiple inheritance.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228479 91177308-0d34-0410-b5e6-96231b3b80d8
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Sean Silva 2015-02-07 01:16:26 +00:00
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docs/HowToSetUpLLVMStyleRTTI.rst
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@ -377,6 +377,20 @@ contract for ``classof`` is "return ``true`` if the dynamic type of the
argument is-a ``C``". As long as your implementation fulfills this
contract, you can tweak and optimize it as much as you want.
For example, LLVM-style RTTI can work fine in the presence of
multiple-inheritance by defining an appropriate ``classof``.
An example of this in practice is
`Decl <http://clang.llvm.org/doxygen/classclang_1_1Decl.html>`_ vs.
`DeclContext <http://clang.llvm.org/doxygen/classclang_1_1DeclContext.html>`_
inside Clang.
The ``Decl`` hierarchy is done very similarly to the example setup
demonstrated in this tutorial.
The key part is how to then incorporate ``DeclContext``: all that is needed
is in ``bool DeclContext::classof(const Decl *)``, which asks the question
"Given a ``Decl``, how can I determine if it is-a ``DeclContext``?".
It answers this with a simple switch over the set of ``Decl`` "kinds", and
returning true for ones that are known to be ``DeclContext``'s.
.. TODO::
Touch on some of the more advanced features, like ``isa_impl`` and