Maxime Janvier

Hi, I have quite a tricky problem, and can't figure out a proper solution. You see, I want to log debug strings in my application, so I wrote a module where the only entry point is a pure method "procedure Log(const LogLevel: TLogLevel; const Str: String);". So the goal would be to only log strings if the logger is set to log at least that log level. That way, I can easily change the logger to only log error strings for example. So far so good. Problem is, when I write things like "Log(llTrace, 'Test ' + GetLastError + BuildStringFromContext); for example, the string will be evaluated wether I log it or not, because the log filter is done inside the function. I was wandering if there was a way to avoid the evaluation of the string when I know I won't log it? Of course the obvious solution would be to write "if CanLog(llTrace) then Log('Test ' + GetLastError + BuildStringFromContext);" But that would be tedious to write, and make the code harder to read. So I though of two possibilities: - First: Using inline function, to replace at compile time the first Log line by the if/then statement. Unfortunately, even with inline function, the arguments are fully eveluated when the function is called (tested). So it's a dead end. - I also though to use a preprocessor macro, to replace at compile time the fist line by the if/then statement, but Delphi doesn't support C/C++ like defines, it can only set/evaluate booleans. So do you think of a solution i could've overlooked? Without any solution, I'll stick to my first Log version, as I value code cleanliness over performance, but it's still a bit frustrating knowing my code will execute instructions for nothing at all if I disable my log.... Regards,

Good points! That would require a bit of work, but might worth it! Thank you very much for your time and thoughts, much appreciated! :)

That's actually good! I think that I'll normally use the Log(LogLevel, MyString), but when obvious optimizations appear, I could add a CanLog to avoid evals in loops... In that way, I can have a proper balance between code cleanliness/ease of reading and performances.

Thanks for these approaches! Unfortunately, the strings (or the functions that'll generate the strings) will still be individually evaluated, if I call Log(ttTrace, [SysErrorMessage(GetLastError)]);, the SysErrorMessage function will still be called.

That would be a solution indeed. But performance-wise, I don't know the cost of anonymous functions.. What if that's called in a loop? Even if it' not called, some memory has to be dynamically allocated for the function code + the captured variables + the cost of capturing those variables... I might do a benchmark for that...