From 2bafd0b3201e3b485f524723cc6b91fa9d8bd859 Mon Sep 17 00:00:00 2001 From: David Blaikie Date: Fri, 21 Sep 2012 17:47:36 +0000 Subject: [PATCH] Document "do not use defaults in covered switch-over-enum" coding standard. llvm-svn: 164389 --- docs/CodingStandards.rst | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/docs/CodingStandards.rst b/docs/CodingStandards.rst index 4f955e3012b..ecd5626eb0d 100644 --- a/docs/CodingStandards.rst +++ b/docs/CodingStandards.rst @@ -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 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 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^