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Document "do not use defaults in covered switch-over-enum" coding standard.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164389 91177308-0d34-0410-b5e6-96231b3b80d8
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David Blaikie 2012-09-21 17:47:36 +00:00
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docs/CodingStandards.rst
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@ -818,6 +818,24 @@ least one out-of-line virtual method in the class. Without this, the compiler
will copy the vtable and RTTI into every ``.o`` file that ``#include``\s the will copy the vtable and RTTI into every ``.o`` file that ``#include``\s the
header, bloating ``.o`` file sizes and increasing link times. header, bloating ``.o`` file sizes and increasing link times.
Don't use default labels in fully covered switches over enumerations
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
``-Wswitch`` warns if a switch, without a default label, over an enumeration
does not cover every enumeration value. If you write a default label on a fully
covered switch over an enumeration then the ``-Wswitch`` warning won't fire
when new elements are added to that enumeration. To help avoid adding these
kinds of defaults, Clang has the warning ``-Wcovered-switch-default`` which is
off by default but turned on when building LLVM with a version of Clang that
supports the warning.
A knock-on effect of this stylistic requirement is that when building LLVM with
GCC you may get warnings related "control may reach end of non-void function"
if you return from each case of a covered switch-over-enum because GCC assumes
that the enum expression may take any representable value, not just those in
the enumeration. To suppress this warning, use ``llvm_unreachable`` after the
switch.
Use ``LLVM_DELETED_FUNCTION`` to mark uncallable methods Use ``LLVM_DELETED_FUNCTION`` to mark uncallable methods
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^