Forum: Ruby Method Auto Completion (#112)

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James G. (Guest)
on 2007-01-25 14:25
(Received via mailing list)
by Robert D.

First of all I would like to thank all submitters.

One of the best features of the Ruby Q. is it tolerance brings up new
ideas so
often.

In order to honor this feature I will first present Daniel F.'s
solution. It
just abbreviates all defined methods. This very useful a feature which I
will
demonstrate after discussion of the code.

  class Object
      def method_missing(method, *args, &blk)
          # Gather all possible methods it could be.
          possibleMethods = self.methods.select {|x|
            x =~ /^#{Regexp.escape(method.to_s)}/
          }
         
          case possibleMethods.size
          # No matching method.
          when 0
              raise NoMethodError.new(
                "undefined method `#{method}' for " +
                "#{self.inspect}:#{self.class.name}"
              )
         
          # One matching method, call it.
          when 1
              method = possibleMethods.first
              send(method, *args, &blk)
         
          # Multiple possibilities, return an array of the
possibilities.
          else
              "Ambigous abbreviation #{method} ->  " +
              "#{ possibleMethods.join(", ")}"
          end
      end
  end

Nothing very complicated there, just define method_missing in Object as
a catch
all for undefined methods in any object. Than he creates an array of all
methods
which are legal completions of a potential abbreviation. In case there
are none
an original NoMethodError is mimicked. In case there is exactly one it
is
executed via send, please note the (method, *args, &blk) syntax, the
&blk part
has been forgotten in some solutions but is vital in #method_missing.
And
eventually if there are more Daniel returned an array of all completions
for
testing. I will discuss this later.

I have adapted this to return a message explaining what completions
exist for
the abbreviation. Why?  Well I just fired up my irb and requested
Daniel's
solution, see what I got, much less typing for free. Here are some
excerpts of
my irb session.

  irb(main):001:0> require 'sol2'
  => true
  irb(main):002:0> "a".le
  => 1
  irb(main):003:0> "abba".le
  => 4
  irb(main):004:0> "Hello World".spl
  => ["Hello", "World"]
  irb(main):005:0> "Hi there Daniel".sp
  => ["Hi", "there", "Daniel"]
  irb(main):006:0> "Hi there Daniel".s
  => "Ambigous abbreviation s ->  select, slice, sub!, squeeze, send,
split,
  size, strip, succ!, squeeze!, sub, slice!, scan, sort, swapcase,
swapcase!,
  sum, singleton_methods, succ, sort_by, strip!"
  irb(main):007:0> 12.x
  NoMethodError: undefined method `x' for 12:Fixnum
                  from ./sol2.rb:9:in `method_missing'
                  from (irb):7

Quite nice as a side product, no?

Let us turn towards solutions which respected the idea of defining
certain
abbreviations, being interpreted in Command Line Interfaces for example.
It was
extremely difficult to chose a solution because most of the solutions
had their
strong parts. I eventually decided to comment on Donald B.'s solution
as it
was maybe the most readable solution for myself. I had discussed this
with James
who favored other solutions for other reasons and I will mention these
reasons
shortly.  As always there is something in every solution so take your
time and
read them.

Ok here is Donald's code - slightly modified again.

  require 'set'

  module AutoComplete
      module ClassMethods
          attr_reader :abbrs
          def abbrev(*args)
              # TODO abbrs might be better implemented as a sorted set
              @abbrs ||= Set.new
              @abbrs += args
          end
      end
      module ObjectMethods
          def method_missing(id, *args, &blk)
              # if it is an exact match, there is no corresponding
method
              # or else it would have been called
              if self.class.abbrs.include?(id)
                  super
              end
              s = id.to_s
              len = s.length
              # find all abbreviations which begin with id and have
              # active methods
              matches = self.class.abbrs.select { |abbr|
                abbr.to_s[0,len] == s && respond_to?(abbr)
              }
              if matches.length == 0
                  super
              elsif matches.length == 1
                  send(matches[0], *args, &blk)
              else
                  matches
              end
          end
      end
  end

  class Object
      extend AutoComplete::ClassMethods
      include AutoComplete::ObjectMethods
  end

Although this can be done more concisely I eventually started to like
the
explicit way.

Lots of little details can be changed and they were in other solutions.
Not
everybody wanted a NoMethodError thrown in case an abbreviation target
was an
abbreviation of a different method and was not there.

Ken B. was the first to point out that it was a bad idea to return an
array
of abbreviations in case of ambiguities. I completely agree, that was
only for
the test code anyway.

A great majority of the solutions follow this idea which is certainly a
must
under some circumstances. I imagine a DSL which is not interactive and
where the
interpreter has no choice than to throw an Exception, good thinking
here.

Ken's solution has three features noteworthy, first he added the list of
possible completions as an attribute of the exception he throws,
secondly he
just used the abbrev Standard Library Module and thirdly he used #super
in
#method_missing to raise a NoMethodError. super in that case calls
Kernel#method_missing. This took me some time to figure out. I guess the
road to
Ruby mastery is not answering quizzes but submitting quizzes and
understanding
the solutions. But you will find some of these features in other
solutions too.

Let us finish the summary with his code, another astonishing example of
how much
can be done with so little code in Ruby.

  require 'abbrev'

  class AmbiguousExpansionError < StandardError
    attr_accessor :candidates
    def initialize(name,possible_methods)
      super("Ambiguous abbreviaton: #{name}\n"+
            "Candidates: #{possible_methods.join(", ")}")
      @candidates=possible_methods
    end
  end

  module Abbreviator
    def method_missing name,*args
      abbrevs=methods.abbrev
      return send(abbrevs[name.to_s],*args) if abbrevs[name.to_s]
      meths=abbrevs.reject{|key,value| key!~/^#{name}/}.values.uniq
      raise AmbiguousExpansionError.new(name, meths) if meths.length>1
      return super(name,*args)
    end
  end

Many thanx to everyone....
James G. (Guest)
on 2007-01-26 15:47
(Received via mailing list)
For those keeping score at home, this message had a bad subject.  It
was the summary to quiz 110, not 112.  I fat-fingered the launch.  My
apologies.

James Edward G. II
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