Currently DebugOnly provides: operator=() operator++() operator--() It would be nice to support operator+=() and operator-=() as well. Stylistically I prefer += to ++ outside of for-loops. I was surprised when DebugOnly += broke in non-DEBUG builds.

Actually, when I try to use this in a build I get a warning: 7:18.26 /srv/mozilla-central/dom/cache/CacheStreamControlParent.cpp:104:22: error: ISO C++ says that th ese are ambiguous, even though the worst conversion for the first is better than the worst conversion fo r the second: [-Werror] 7:18.26 In file included from ../../dist/include/ipc/IPCMessageUtils.h:14:0, 7:18.26 from /srv/mozilla-central/obj-x86_64-unknown-linux-gnu-debug/ipc/ipdl/_ipdlheaders/mozilla/dom/cache/PCacheStreamControl.h:12, 7:18.26 from /srv/mozilla-central/obj-x86_64-unknown-linux-gnu-debug/ipc/ipdl/_ipdlheaders/mozilla/dom/cache/PCacheStreamControlParent.h:9, 7:18.26 from ../../dist/include/mozilla/dom/cache/CacheStreamControlParent.h:10, 7:18.26 from /srv/mozilla-central/dom/cache/CacheStreamControlParent.cpp:7: 7:18.26 ../../dist/include/mozilla/DebugOnly.h:54:14: note: candidate 1: mozilla::DebugOnly<T>& mozilla::DebugOnly<T>::operator+=(const T&) [with T = unsigned int; mozilla::DebugOnly<T> = mozilla::DebugOnly<unsigned int>] 7:18.26 /srv/mozilla-central/dom/cache/CacheStreamControlParent.cpp:104:22: note: candidate 2: operator+=(unsigned int&, int) <built-in>

Ugh.

So the solution is just to provide the operator+=() and operator-=() in non-debug builds. When DEBUG is defined then the implicit cast operator allows the built-in += and -= to be used.

Comment on attachment 8549842 [details] [diff] [review] Add operator+=() and operator-=() to DebugOnly (v1) Review of attachment 8549842 [details] [diff] [review]: ----------------------------------------------------------------- r=me with the change below: ::: mfbt/DebugOnly.h @@ +66,5 @@ > DebugOnly& operator=(const T&) { return *this; } > void operator++(int) { } > void operator--(int) { } > + DebugOnly& operator+=(const T&) { return *this; } > + DebugOnly& operator-=(const T&) { return *this; } Can you add a comment describing why we define these in this arm of the #ifdef, but not in the previous arm?

With requested comment: https://hg.mozilla.org/integration/mozilla-inbound/rev/7a80f8e49992

Apparently the world is not ready for ooperators: https://hg.mozilla.org/integration/mozilla-inbound/rev/ef8894863cdf

https://hg.mozilla.org/mozilla-central/rev/7a80f8e49992 https://hg.mozilla.org/mozilla-central/rev/ef8894863cdf