simple hash merge by array of keys and values in ruby (with perl example)

Question

In Perl to perform a hash update based on arrays of keys and values I can do something like:

@hash{'key1','key2','key3'} = ('val1','val2','val3');

In Ruby I could do something similar in a more complicated way:

hash.merge!(Hash[ *[['key1','key2','key3'],['val1','val2','val3']].transpose ])

OK but I doubt the effectivity of such procedure.

Now I would like to do a more complex assignment in a single line.

Perl example:

(@hash{'key1','key2','key3'}, $key4) = &some_function();

I have no idea if such a thing is possible in some simple Ruby way. Any hints?

For the Perl impaired, @hash{'key1','key2','key3'} = ('a', 'b', 'c') is a hash slice and is a shorthand for something like this:

$hash{'key1'} = 'a';
$hash{'key2'} = 'b';
$hash{'key3'} = 'c';

Answer 1

In Ruby 1.9 Hash.[] can take as its argument an array of two-valued arrays (in addition to the old behavior of a flat list of alternative key/value arguments). So it's relatively simple to do:

mash.merge!( Hash[ keys.zip(values) ] )

I do not know perl, so I'm not sure what your final "more complex assignment" is trying to do. Can you explain in words—or with the sample input and output—what you are trying to achieve?

Edit: based on the discussion in @fl00r's answer, you can do this:

def f(n)
  # return n arguments
  (1..n).to_a
end

h = {}
keys = [:a,:b,:c]
*vals, last = f(4)
h.merge!( Hash[ keys.zip(vals) ] )
p vals, last, h
#=> [1, 2, 3]
#=> 4
#=> {:a=>1, :b=>2, :c=>3}

The code *a, b = some_array will assign the last element to b and create a as an array of the other values. This syntax requires Ruby 1.9. If you require 1.8 compatibility, you can do:

vals = f(4)
last = vals.pop
h.merge!( Hash[ *keys.zip(vals).flatten ] )

Answer 2

You could redefine []= to support this:

class Hash
  def []=(*args)
    *keys, vals = args # if this doesn't work in your version of ruby, use "keys, vals = args[0...-1], args.last"
    merge! Hash[keys.zip(vals.respond_to?(:each) ? vals : [vals])]
  end
end

Now use

myhash[:key1, :key2, :key3] = :val1, :val2, :val3
# or
myhash[:key1, :key2, :key3] = some_method_returning_three_values
# or even
*myhash[:key1, :key2, :key3], local_var = some_method_returning_four_values