From: Daniel Berger <djberg96@...>
Date: 2007-08-30T11:21:38+09:00
Subject: Re: Whatever happened to have_const?

Nobuyoshi Nakada wrote:
> Hi,
> 
> At Thu, 30 Aug 2007 05:29:57 +0900,
> Daniel Berger wrote in [ruby-core:12027]:
>> What ever happened to the have_const patch that was supposed to get 
>> added to mkmf.rb?
> 
> Sorry, but nothing yet.
> 
>> I ask because I've hit yet another scenario where I need to check for an 
>> enum value.
>>
>> BTW, there's a bug in that diff - the word "type" should be replaced 
>> with "const".
> 
> For the case of non-integral value as asked by Matz in
> [ruby-core:04428], I'd change the check code like this.
> 
> If no objection, I want to commit it to 1.8 and trunk.
> Any thoughts?

Looks good!

> def try_const(const, header = nil, opt = "", &b)
>   const, type = *const
>   if try_compile(<<"SRC", opt, &b)
> #{COMMON_HEADERS}
> #{cpp_include(header)}
> /*top*/
> typedef #{type || 'int'} conftest_type;
> conftest_type conftestval = #{type ? '' : '(int)'}#{const};
> SRC
>     $defs.push(format("-DHAVE_CONST_%s", const.strip.upcase.tr_s("^A-Z0-9_", "_")))
>     true
>   else
>     false
>   end
> end
> 
> # Returns whether or not the constant +const+ is defined.  You may
> # optionally pass the +type+ of +const+ as <code>[const, type]</code>,
> # like as:
> #
> #   have_const(%w[PTHREAD_MUTEX_INITIALIZER pthread_mutex_t], "pthread.h")
> #
> # You may also pass additional +headers+ to check against in addition
> # to the common header files, and additional flags to +opt+ which are
> # then passed along to the compiler.
> #
> # If found, a macro is passed as a preprocessor constant to the compiler using
> # the type name, in uppercase, prepended with 'HAVE_CONST_'.
> #
> # For example, if have_const('foo') returned true, then the HAVE_CONST_FOO
> # preprocessor macro would be passed to the compiler.
> #
> def have_const(const, header = nil, opt = "", &b)
>   checking_for checking_message([*const].compact.join(' '), header, opt) do
>     try_const(const, header, opt, &b)
>   end
> end

Should it be "header" (singular) or "headers" (plural)? If more than one 
header is allowed, I think a cpp_include is required in the try_const 
method.

If not, then the docs for have_const need a minor adjustment.

Regards,

Dan