From: William Fulton <lists@...>
Date: 2013-04-06T21:53:06+09:00
Subject: Re: C API version / functionality detection

Macros containing text such as RUBY_VERSION can't be usefully used by 
the C preprocessor, but the numeric ones such as RUBY_API_VERSION_CODE 
or the old RUBY_VERSION_CODE can be. However, they are in version.h 
which poses two problems. First this file isn't always shipped (eg in 
some Debian based system, such as ruby-1.9.0 on Ubuntu 10.04). Secondly 
in order to get the macro one needs a '#include "version.h"' which is a 
rather commonly named file name, so it may pick up some other version.h 
file which is no good at all as our users are expected to use their own 
code.

Anyway, I've fixed the problem above as rb_respond_to changed in a 
subtle way in 1.9 and the '== Qtrue' should be dropped to check for 
success.

Even so, it is still nearly impossible to write extensions using new 
APIs if one cannot reliably determine if a new API is available or 
detect the version that they might have changed in.

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