On Thu, Jan 15, 2015 at 4:11 PM, Beman Dawes
GCC and Clang have had a warning for years (-Wshadow): "Warn whenever a local variable or type declaration shadows another variable, parameter, type, class member (in C++), or instance variable (in Objective-C) or whenever a built-in function is shadowed. Note that in C++, the compiler warns if a local variable shadows an explicit typedef, but not if it shadows a struct/class/enum."
VC++ 2015 (aka 14.0) Preview has now added a similar warning, C4459. For example, "c:\boost\modular\develop\boost\lexical_cast\detail\converter_lexical_streams.hpp(429): warning C4459: declaration of 'n' hides global declaration". The VC++ warning also provides location info so is easy to view both the declarations involved. In this case, the declaration "bool operator<<(short n)" is shadowing a variable name in the unnamed namespace of the calling translation unit.
The process of clearing these shadow warnings occasionally finds bugs that are otherwise difficult to detect. Peter Dimov and I have both found bugs in our code in the process of clearing the new C4459 warning. Even though most of the warnings don't actually signify bugs, I'm finding that clearing them makes code clearer and less confusing, particularly code I haven't looked at in a long while.
Should Boost have policy to clear these warnings?
A lot of the warnings involve function argument names. Should we have a guideline to prevent shadow warnings? A convention for argument names would make it easier to submit pull requests. Possible guidelines:
* Prefix function argument names with "a_". Rationale: The "m_" prefix for member names has been a success. * Suffix function argument names with "_". Rationale: Short and less distracting than "m_" prefix.
Thoughts?
Despite that the warnings should probably be fixed, I don't think there is need for a naming policy. I'm sure any guideline will contradict someone's habits or preferences, and will be difficult to maintain. Besides it's not clear what to do with tons of written code - starting a new convention without converting the existing code is hardly an improvement. As for the particular issue, it's probably better to mangle the global variable names (my preference is "g_") rather than function arguments or local variables. Globals are much more rare and their names should be chosen carefully anyway.