Alias for array or hash element in Ruby

Question

Example for array

arr = ["a", "b", "c"]
# TODO create an alias for arr[1] as x
x = "X"
# arr should  be ["a", "X", "c"] here

Example for hash

hash = { :a => "aaa", :b => "bbb" , :c => "ccc" }
# TODO create an alias for hash[:b] as y
y = "YYY"
# hash should be { :a => "aaa", :b => "YYY" , :c => "ccc" } here

And also an alias for a variable?

var = 5
# TODO create an alias for var as z
z = 7
# var should be 7 here

Motivation: I have a big large deep construct of data, and you can imagine the rest. I want to use it in a read-only manner, but due to performance reasons copy is not permissible.

Metaphor: I want to choose context from a larger data structure and I want to access it with a short and simple name.

UPDATE: Problem solved as sepp2k advised. I just want to draw a summarizing picture here about the solution.

irb(main):001:0> arr = [ { "a" => 1, "b" => 2}, { "x" => 7, "y" => 8 } ]
=> [{"a"=>1, "b"=>2}, {"x"=>7, "y"=>8}]
irb(main):002:0> i = arr[0]
=> {"a"=>1, "b"=>2}
irb(main):004:0> j = arr[1]
=> {"x"=>7, "y"=>8}
irb(main):007:0> j["z"] = 9
=> 9
irb(main):008:0> j
=> {"x"=>7, "y"=>8, "z"=>9}
irb(main):009:0> arr
=> [{"a"=>1, "b"=>2}, {"x"=>7, "y"=>8, "z"=>9}]

sepp2k · Accepted Answer · 2010-10-18 15:05:02Z

4

What you want is not possible. There is no feature in ruby that you could use to make your examples work like you want.

However since you're saying you want to only use it read-only, there is no need for that. You can just do x = myNestedStructure[foo][bar][baz]. There will be no copying involved when you do that. Assignment does not copy the assigned object in ruby.

answered Oct 18, 2010 at 15:05

sepp2k

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Comments

Jeremy · Accepted Answer · 2010-10-18 15:10:22Z

2

You would have to create a method that is your alias, which would update the data.

def y=(value)
  arr[:b]=value
end

Then call it.

self.y="foo"

Edit: updated second code snippet.

answered Oct 18, 2010 at 15:10

Jeremy

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2 Comments

sepp2k Over a year ago

No, you can't. You can call it with self.y = "foo", but not with y = "foo". y = "foo" will always assign to the local variable y, no matter what setter methods are defined.

August Lilleaas Over a year ago

2nd snippet needs to be self.y = foo, or else the local variable y is assigned, even when the method y is in scope.

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