From: Paul Brannan <pbrannan@...>
Date: 2002-06-03T22:49:33+09:00
Subject: Re: Does assert() exist?

On Mon, Jun 03, 2002 at 08:10:59PM +0900, Damon wrote:
> This is very nice, but I wonder if Ruby can simulate a stringizing
> assert macro from C, which I find more elegant:
> 
> #define assert(x)(x || fprintf(stderr, "Assertion failed: %s\n", #x))

I sometimes do something like this:

  $initial_directory = Dir.getwd

  def caller_file_pathname(filename)
    File.expand_path(filename, $initial_directory)
  end

  def parse_caller(caller_str)
    file, lineno, method = caller_str.split(':')
    if method =~ /in `(.*)'/ then
      method = $1.intern()
    end
    return file, lineno.to_i(), method
  end

  def caller_line(level=0)
    dir = File.dirname(caller_file_pathname($0))
    file, lineno, method = parse_caller(caller[level.succ])
    File.open(File.expand_path(file, dir)) do |input|
      (lineno.to_i - 1).times { input.gets }
      return input.gets
    end
  end

  if DEBUG then
    def assert(x, msg=nil)
      if not x then
        failed_msg = msg.nil? \
          ? caller_line().sub(/^\s*/, '').chomp \
          : msg
        puts "Assertion failed: #{failed_msg}"
      end
    end
  else
    def assert(x, msg=nil)
    end
  end

but usually using one of the test libraries (Test::Unit, Rubyunit,
Lapidary) is sufficient; assert_equal prints a MUCH more useful message
than the above code.

Paul