From: Rosalind Mitchell <rcmitchell@...>
Date: 2011-12-07T04:09:06+09:00
Subject: Developing Qt4 applications with Ruby 1.9.x

I am running KDE on 32-bit Linux Mint Debian Edition.  For several years now I 
have been developing Qt-based applications with Ruby 1.8.

Now I'm anxious to move forward and adopt Ruby 1.9 as urged.  I can install 
1.9.2 from the LMDE repositories, but there doesn't appear to be any Qt4 
libraries available.  So I thought I'd go right up to date, downloading and 
compiling Ruby 1.9.3p0 from scratch, installing it in the /usr/local 
hierarchy.

I found, downloaded and extracted the latest Qt4-QtRuby build files.  This is 
where the headaches began.  Running cmake . failed immediately as cmake could 
not find Ruby.  After scratching my head and searching Google I established 
that the CMakeCache.txt file needed some tweaking.  To be precise, these lines 
needed to be filled out to allow cmake to find the ruby.h file and ruby 
executable:

//Path to a file.
RUBY_CONFIG_INCLUDE_DIR:PATH=/usr/local/include/ruby-1.9.1/i686-linux

//Path to a program.
RUBY_EXECUTABLE:FILEPATH=/usr/local/bin/ruby

This, then, allowed me to build and install the Qt4-QtRuby library.  But then, 
when I went to test it with a very minimal script:

#!/usr/local/bin/ruby -w

require 'Qt4'

app = Qt::Application.new(ARGV)

app.exec()

I get the response:

/usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:1415: warning: mismatched 
indentations at 'end' with 'if' at 1411
/usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2527: warning: method 
redefined; discarding old method_missing

[...]

/usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2527: warning: method 
redefined; discarding old const_missing
/usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:459:in `initialize': 
unresolved constructor call Qt::Application (ArgumentError)
        from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:459:in 
`initialize'
        from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2640:in `call'
        from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2640:in `block 
in try_initialize'
        from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2639:in `catch'
        from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2639:in 
`try_initialize'
        from ./qt.rb:16:in `new'
        from ./qt.rb:16:in `<main>'

(that second warning repeated several hundred times, though I'm not all that 
concerned about that.)

The test script works fine under 1.8.7, obviously it doesn't do anything but it 
doesn't throw any warnings or errors either.

Doing the same in irb yields

irb(main):001:0> require 'Qt4'
=> true
irb(main):002:0> app = Qt::Application.new(ARGV)
ArgumentError: unresolved constructor call Qt::Application

        from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:459:in 
`initialize'
        from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:459:in 
`initialize'
        from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2640:in `call'
        from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2640:in `block 
in try_initialize'
        from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2639:in `catch'
        from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2639:in 
`try_initialize'
        from (irb):2:in `new'
        from (irb):2
        from /usr/local/bin/irb:12:in `<main>'
irb(main):003:0> 

Enquiries on Google haven't been very fruitful, with just a suggestion that 
the fault lies in the Qt.cpp file but not much help that I could see on exactly 
what the problem is or how to fix it (my knowledge of C++ is sketchy at best).

I have the feeling either that I've missed something very simple, or that Ruby 
1.9.x is not yet able to work effectively with Qt4.  Is there anybody here who 
has encountered this problem?  Should I carry on regardless with 1.9.3 and find 
another GUI interface to work with, or should I reluctantly revert to 1.8.7?

Rosie


-- 
Mój poduszkowiec jest pełen węgorzy
Currently reading Headlong by Michael Frayn