Disabling string evaluation in a logging system

[dhenry <tfc.duke@gmail.com>]

Hello,

I have a logging system controlled by a log level (let's say 0 =
disabled, 1 = errors, 2 = error + warnings, ..., 5 = all previous ones
+ debug messages).

A Logging line may look like that:

Log.Write (Text => "Blabla...", Level => 5);

Often, I'll have some formatted text, requiring string conversions and
concatenations. Example:

Log.Write ("Parameter " & To_String (Param_Name) & " Value = " &
Integer'Image (X), Log_Level);

If the Log_Level variable is set to 0 (logging disabled), the
application will still evaluate the Text parameter, before testing the
Level parameter to know if we finally must write it into the file or
not.

I'd like to avoid the string evaluation if the logging is disabled
(because it consumes CPU resources).

A possible solution would be to test the log level before the
procedure call:

if Log_Level > 0 then
  Log.Write ("Parameter " & To_String (Param_Name) & " Value = " &
Integer'Image (X), Log_Level);
end if;

But with thousands of logging lines everywhere in my application, it
will make the code quite unreadable and introduces a lot of if-test
pollution (and it's really boring to write).

In a language like C or C++, I would use the preprocessor:
#define LOG(text, level) if (level > 0) { log.write (text, level) }

I'm wondering how in Ada 95 and/or Ada 2005 I could write such a
logging system (if it's possible). The goal is that logging should not
be too intrusive in my code.

Yours,
David.