From: "Peña, Botp" <botp@...>
Date: 2007-10-11T10:36:24+09:00
Subject: Re: will #in? be in ruby2? (was Re: Finding shared elements between to arrays.)

From: Alex Gutteridge
# Daniel's point (I think) is that this pollutes the top 
# level Object with a property which for many (most?) 
# Objects is never relevant. If 

arggh, i wish we could measure that "pollution". (sometimes, i even includes Trans's facets gem of extensions :) My addition of it is not about polluting, it's about me expressing my thoughts well in a program. I thought in? would include just a very small helpful code.
 
# you never put it an Object into a collection then 
# the idea of being 'in' something makes no sense.

well i thought that all objects in ruby can be put into a container, so i reckon #in? (like #include?) would be very handy too. I use it many times.

# On the other hand it is always an intrinsic part 
# of an Enumerable implementing class (by definition
# a collection of Objects) that you may often need to 
# know whether it 'includes' a specified object.

no problem there.

# I'm not sure why the includes construct rocks your brain 
# though. Both read very logically to me (as a native 
# English speaker admittedly):
# 
# a3 = a1.select { |e| a2.include?(e) }
# 
# reads as: 'select' from a1 those e where a2 'includes' e.
# 
# a3 = a1.select { |e| e.in? a2}
# 
# reads as: 'select' from a1 those e where e is 'in' a2.

i'm reading it again, and i still find the second one much better to read, it's straightforward and you can read it fast.

try reading it like in math or in symbolic logic,

  {|e| e.in? a}

  read: "e such that e is in a"

whereas

  {|e| a.in? e}

  read: "e such that a includes e"

  suddenly, my point of (object) reference changes from e to a and from left to right. which is kind of weird to me assumming I were to right it in a technical report.

I would use include? and in? like the ff,

  {|a| a.include? e}

  {|e| e.in? a}

  note the similarity and difference. clear reading left to right. Clearly, if there's a place for include?, there is too for in?.


# That said I always write this as:
# a3 = a1 & a2

that was just a simple example (and besides, i'm not even sure they are the same) to show difference bw include? and in?.

kind regards -botp