Question

作为磁悬浮的新手，我想从一个小但仍然有用的例子开始。所以我决定开始移动我用来生成磁悬浮发票的ruby类。但是我使用（优秀的）PDF库存在意外问题。

在rvm上我为应用程序生成了一个gemset，它在.rvmrc中为invoice目录设置。当我进入它时它会被使用：

Using /Users/patru/.rvm/gems/maglev-head with gemset invoice

当我安装大虾时，一切都很好，宝石似乎已经安装好了，并且正在生成ri-docs。但是，当应该创建rdoc时会出现问题，maglev提供的gem命令会给我

 gem install prawn
[INFO] The MagLev team publishes customized versions of some gems.
...
Successfully installed prawn-0.12.0
1 gem installed
Installing ri documentation for prawn-0.12.0...


RDoc failure in lib/prawn/images/jpg.rb at or around line 20 column 26

Before reporting this, could you check that the file
you're documenting compiles cleanly--RDoc is not a
full Ruby parser, and gets confused easily if fed
invalid programs.

The internal error was:

ERROR:  While generating documentation for prawn-0.12.0
... MESSAGE:   global $@ is a read-only variable
... RDOC args: --ri --op /Users/patru/.rvm/gems/maglev-head@invoice/doc/prawn-0.12.0/ri --title Prawn Documentation --main README -q lib README.md LICENSE COPYING GPLv2 GPLv3 --title prawn-0.12.0 Documentation --quiet
a RubySystemExit occurred (error 2752)

没有文档就没什么大不了的，这已经足够了，但其他东西似乎出了问题，宝石列表说

Ascii85 (1.0.1)
bundler (1.0.21)
erector (0.8.3)
pdf-reader (0.10.1)
polyglot (0.3.3)
prawn (0.12.0)
rake (0.9.2)
treetop (1.4.10)
ttfunk (1.0.3)

所以一切似乎都很好，但如果我这样做

require 'ruby gems'
require 'prawn'

in irb（在我的ree-1.8.7上完美运行）我得到一个奇怪的

NoMethodError: NoMethodError: undefined method `ruby_18' for 
from /Users/patru/.rvm/gems/maglev-head@invoice/gems/prawn-0.12.0/lib/prawn/core/object_store.rb:246:in `__compileClass'
from /Users/patru/.rvm/gems/maglev-head@invoice/gems/prawn-0.12.0/lib/prawn/core/object_store.rb:14:in `__compileClass'
from /Users/patru/.rvm/gems/maglev-head@invoice/gems/prawn-0.12.0/lib/prawn/core/object_store.rb:13:in `__compileClass'
from /Users/patru/.rvm/gems/maglev-head@invoice/gems/prawn-0.12.0/lib/prawn/core/object_store.rb:12
from /Users/patru/.rvm/rubies/maglev-head/src/kernel/bootstrap/Kernel.rb:831:in `gem_original_require'
from /Users/patru/.rvm/rubies/maglev-head/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `require'
from /Users/patru/.rvm/rubies/maglev-head/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:57:in `require'
from /Users/patru/.rvm/gems/maglev-head@invoice/gems/prawn-0.12.0/lib/prawn/core.rb:78
from /Users/patru/.rvm/rubies/maglev-head/src/kernel/bootstrap/Kernel.rb:831:in `gem_original_require'
from /Users/patru/.rvm/rubies/maglev-head/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `require'
from /Users/patru/.rvm/rubies/maglev-head/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:57:in `require'
from /Users/patru/.rvm/gems/maglev-head@invoice/gems/prawn-0.12.0/lib/prawn.rb:11
from /Users/patru/.rvm/rubies/maglev-head/src/kernel/bootstrap/Kernel.rb:831:in `gem_original_require'
from /Users/patru/.rvm/rubies/maglev-head/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:59:in `require'
from /Users/patru/.rvm/rubies/maglev-head/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:57:in `require'
from /Users/patru/.rvm/rubies/maglev-head/src/kernel/bootstrap/Kernel.rb:831:in `gem_original_require'
from /Users/patru/.rvm/rubies/maglev-head/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `require'
from /Users/patru/.rvm/rubies/maglev-head/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:57:in `require'
from (irb):5:in `__compileEval'
from (irb):7:in `__compileEval'
from /Users/patru/.rvm/rubies/maglev-head/src/kernel/bootstrap/Kernel.rb:394:in `eval'
from /Users/patru/.rvm/rubies/maglev-head/lib/ruby/1.8/irb.rb:159:in `eval_input'
...

我可能在这里遗漏了一些明显的东西。我只想说这个“架设者”就足够了。我安装的宝石（见上面的宝石清单）可以毫无问题地要求，所以我不会做错事; - ）

Answer 1

这似乎是与irb的互动。我可以运行以下脚本并创建正确的pdf文件：

require 'rubygems'
require 'prawn'

Prawn::Document.generate('hello.pdf') do
  text "Hello! from #{RUBY_ENGINE}"
end

最好在https://github.com/maglev/maglev/issues

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如何在磁悬浮上使用虾

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