5.next=6, what about 5.prev ??

[phpsharma]

Hi,

There is a method called next for fixnum to get next number. Whats the method to get previous number.

I need a straight method if any. I searched manual and not found one..

I hope this will give a thought..

number=5
number.next=6

to get 4 , which method i need to use..?. I need a straight method not alternatives..?

Thanks,
Sharma

[vgarcia]

There is no prev/previous method. You'd have to write it yourself. Fortunately it's really easy to do:

number = 5
number.next #6

class Fixnum
  def prev
    self - 1
  end
end

number.prev #4

[phpsharma]

Yeah..That can be possible. But why matz(ruby creator) missed this kind of method by default?

[Fenrir2]

succ() is used by ranges (similar to next()), I think that's why has been added. If you create a range: (3..10) and iterate over it, Ruby calls the succ() method of 3 until it's 10. That's why you can have ranges of strings or ranges of your own objects.

If you're going to implement prev() you should probably create an alias named pred():

succ <=> pred
next <=> prev

[vgarcia]

Yeah..That can be possible. But why matz(ruby creator) missed this kind of method by default?

Maybe because

variable - 1

is more concise and less verbose than

variable.prev

To be honest I'd ask the reverse question had Fenrir2 not answered it already: why next() at all?

[phpsharma]

Thank you Fenrir2 & vgarcia,

vgarcia: You are correct. When we can do with variable+1 why next method for fixnum?

I hope some extra benifit is there. with next? Just a curious question.

Sharma

[Fenrir2]

The pred and succ are polymorphic: they work on strings, numbers, or any type that defines the method. +1 and -1 only work on numbers.

why next() at all?

This is a very good question anyway: why does Ruby have so many method aliases? map/collect for example: collect from smalltalk and map from scheme (or maybe from another functional language?). I prefer to use map because it sounds less iterative than collect; more like an atomic operation. People who are used to imperative languages will probably prefer collect. Why does Ruby have these aliased methods at all? (it's not even consistent: there is inject from Smalltalk, but not reduce (from Scheme) or foldl (from Haskell)). This is one thing I don't like about Ruby. TIMTOWTDI is good, but not in this case?