From: Phlip <phlipcpp@...>
Date: 2006-10-24T23:05:14+09:00
Subject: assertion reflection

[X-posted from the RSpec mailing list]

We discuss RSpec's assertions, which use 'should' for 'assert'.

Micah Martin wrote:

> x.should_equal 2
> a.should_not_be nil

> When they fail they yield messages like:

> 1 should equal 2
> nil should not be nil

> In my humble opinion, these messages should include their context and read
> like this:
>
> x should equal 2 but was 1
> a should not be nil but was nil

This is why C++ is superior to Ruby. An assertion can reflect its expression 
into the diagnostic report like that.

Oh, and I mis-Googled this subject recently, and inadvertently learned that 
Python assertions now supports that reflection.

If I tell the maintainers that C++ can do something, they'l ignore me. But 
if I say Python can, they will doubtless see red and go crazy about it.

Here's a snip of research that might still work:

def trace_(&b)
        file, line_nr, funkshun = caller()[0].split(':')

  #  sorry, folks - split's the only stringey function I know ;-)

        funkshun = funkshun.split(/in `/)[1]
        funkshun = funkshun.split(/\'/)[0]
        line_nr=line_nr.to_i
        linecnt=1
        expr=nil

        File.open(file).each_line do |line|
                if linecnt==line_nr
                        if line =~ /(^|\W)trace_\s*\{\s*(.*?)\s*\}/
                                expr = $2
                        end
                        break
                end
                linecnt+=1
        end

        if expr
                print file
  puts "(#{line_nr})#{funkshun} #{expr}: #{eval(expr, b).inspect}"
        end #{file}
end

The intent was to let trace_{foo} reflect both foo and its value.

RSpec could get by with fewer fragile regular expressions, and could simply 
reflect its entire line, then tack the variables on the end:

  x.should_equal 2 (1, 2)

-- 
  Phlip
  http://c2.com/cgi/wiki?ZeekLand  <-- NOT a blog!!