Aside: As opposed to using the build system or the template processor which are totaly different except in the ways they are completely the same.
Languages with C-derived syntax and exceptions generally have a try-catch construct and the ones I'm familiar with have a little trap for the inattentive programmer: the catch block is a different scope from the try blocks. Which means when you merrily write
try {
ErrorInfo e;
someRiskyOperation(e)
} catch (...) {
print("Risky operation failed with error %s\n",e.explanation());
}
because the argument to someRiskyOperation is an out-param1 and you hope to capture the error data that was generated before the exception was thrown, you actually get a compilation error because e isn't in scope when you try to issue the message.
Not a big problem, of course, at least two work-around are obvious.
Except that I tried to send a message to our logger, so the code looked like
try {
ErrorInfo e;
someRiskyOperation(e)
} catch (...) {
LOG_WARN("Risky operation failed with error " + e.explanation());
}
where LOG_WARN is a macro whose purpose is to capture the file and line where the error occured.2 And that's a problem if this code occurs in a library that can be compiled with logging support turned off by simply defining the logging macros as nulls: #define LOG_WARN(explanation) , because in that case the compiler never sees the offending e.explanation. It was rewritten as nothing even before lexing. So you can test the code with logging turned off to your hearts content and never find the bug. Sigh.
1 Yes, I agree: out-params are generally evil. It's a legacy API. Perhaps we'll get around to replacing it eventually.
2 When it actually does something it looks something like
#define LOG_WARN(explanation) do { \
logger:Message logmsg(__FILE__, __LINE__, explanation, logger::Warning); \
logger::getLogHandler().post(logmsg); \
while(false)
and it can't be a function because __FILE__ and __LINE__ are macros and have to be evaluated in place. Unless and until the language provides operators for capturing source position data like that this is the best we can do.
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