From: Robert Klemme <bob.news@...>
Date: 2004-01-28T01:44:55+09:00
Subject: Re: newbee question about "missing" hash methods +, += and <<


"benny" <linux@marcrenearns.de> schrieb im Newsbeitrag
news:20040127171647.756933c0@bava.ho...
> Hi,
>
> I'm wondering if there is a special reason for the class Hash not to
have the methods +, += and <<
> just like Array.

First of all, no class has a method "+=".  Instead this is a syntactic
shortcut that transforms "a += b" into "a = a + b" - whatever 'a' and 'b'
are.

> I would find it intuitive if I could do something like this
>
> testhash = Hash.new
> testhash << {"some key" => "some value"}

There is "update":

irb(main):004:0> testhash = {}
=> {}
irb(main):005:0> testhash.update( {"some key" => "some value"} )
=> {"some key"=>"some value"}
irb(main):006:0> testhash
=> {"some key"=>"some value"}

> secondhash = {"some other key" => "some other value"}
> testhash += secondhash
> #->  {"some key" => "some value", "some other key" => "some other
value"}

irb(main):007:0> secondhash = {"some other key" => "some other value"}
=> {"some other key"=>"some other value"}
irb(main):008:0> testhash.update secondhash
=> {"some other key"=>"some other value", "some key"=>"some value"}

> thats the behaviour of arrays and I know that I could extend the class
Hash, so that its supported.
> I simply want to know if there is a special reason why it is not
supported by default.

I guess it's that Hash#update is peculiar because it depends on which hash
is updated by the other, which is important if both Hashes share some
keys.  Apart from that Hash#+ might be a bit inefficient in situations
where you want to update a Hash via +=.

class Hash
  def +(h)
    dup.update(h)
  end
end

a = {}
b = {}

a += b

# in reality:
# tmp = a + b
# a = tmp
# old a is dropped

Kind regards

    robert