[ruby-talk:8786] Re: No :<, :>, etc. methods for Array

In article <[e-mail]>,
Brian F. Feldman <[e-mail]> wrote:
....
>I know you can define sum in terms of inject, but what is the point of 
>having inject if people are just going to use it to create sum?

It can also be used to create product (also very important), and, if the
definition is done  the right way one also gets  alternating sums (using
'-'). One  can also  get continued  fractions, min and  max of  an array
(from min and max of 2 elements), intersection of a family of sets (with
'&'), etc...

 Note  that a  direct call  to  inject has  an advantage  over sum:  the
neutral element for the operation can be specified; so a call to

  a.inject(0){|n, value| n + value}

works even for empty a (contrary to your proposed definition). Also

  a.inject(""){|n, value| n + value}

does join for string arrays.

 I  learned the  usefulness  of inject  while working  with  APL in  the
seventies (yes, I am *that* old...)  where it was called "reduce". Thus,
I also propose 'reduce' as a name for inject.

 While I am at it, I would like to mention something I wish for ruby: in
APL or in more modern languages  with a functional flavour, you can just
write  '+' for  the  block {|a,b|  a+b}. I  wish  something similar  was
possible in ruby so one could just write

  a.reduce(0,+)

instead of the above -- or perhaps more realistically:

  a.reduce(0,:+)

It would also have the advantage to be able to easily (hum, I don't know
about  that, I  have not  yet learned  ruby internals)  implement kernel
optimizations of the above call when the argument '+' is itself a kernel
function (would  not you dream to  be able to write  ruby programs which
run  faster than  fortran,  as  was possible  in  APL  by using  similar
tricks?).

Best regards,
  Jean MICHEL