From: Brian Candler <b.candler@...>
Date: 2010-02-23T01:46:09+09:00
Subject: Re: Binding#eval issue

Thomas Sawyer wrote:
> I have the following extensions to Binding:
> 
>   class Binding
> 
>     # Returns line number of the binding.
>     def __LINE__
>       eval("__LINE__")
>     end
> 
>     # Returns file name of the binding.
>     def __FILE__
>       eval("__FILE__")
>     end
> 
>   end
> 
> The work fine in 1.8.7

I tried this, and was surprised to find that 1.8.7 makes a special case 
of eval inside an instance method of Binding:

$ irb --simple-prompt
>> RUBY_VERSION
=> "1.8.7"
>> RUBY_PATCHLEVEL
=> 174
>> class Binding; def __LINE__; eval "__LINE__"; end; end
=> nil
>> class Binding; def __FILE__; eval "__FILE__"; end; end
=> nil
>> binding.__LINE__
=> 6
>> binding.__LINE__
=> 7
>> binding.__FILE__
=> "(irb)"
>> binding.__FILE__
=> "(irb)"

This is particularly surprising given that instance_eval doesn't show 
this behaviour:

>> binding.instance_eval "__LINE__"
=> 1
>> binding.instance_eval "__LINE__"
=> 1
>> binding.instance_eval "__FILE__"
=> "(eval)"
>> binding.instance_eval "__FILE__"
=> "(eval)"

__FILE__ is the filename where the source being executed is found. When 
eval'ing from a string, the source is not in any particular file and so 
I'd always expect "(eval)" to be returned, and __LINE__ to be relative 
to the start of the string, unless you pass file and/or line numbers as 
extra args to eval.

In ruby 1.9.2 this works as I'd expect:

$ irb19 --simple-prompt
>> RUBY_REVISION
=> 24186
>> class Binding; def __LINE__; eval "__LINE__"; end; end
=> nil
>> class Binding; def __FILE__; eval "__FILE__"; end; end
=> nil
>> binding.__LINE__
=> 1
>> binding.__LINE__
=> 1
>> binding.__FILE__
=> "(eval)"
>> binding.__FILE__
=> "(eval)"

So I'd say that 1.8.7 is the anomoly.
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