Quickly setting instance variables with options hash in Ruby?

Question

I want to use an options hash as input to a method in Ruby, but is there a way to quickly set all eponymous variables (i.e having the same name) instead of setting each individually?

So instead of doing the following:

class Connection
  def initialize(opts={})
    @host     = opts[:host]
    @user     = opts[:user]
    @password = opts[:password]
    @project  = opts[:project]
    # ad nauseum...

is there a one-liner that will assign each incoming option in the hash to the variable with the same name?

possible duplicate of [in Ruby can I automatically populate instance variables somehow in the initialize method?](http://stackoverflow.com/questions/9597249/in-ruby-can-i-automatically-populate-instance-variables-somehow-in-the-initializ) — mydoghasworms, Nov 09 '12 at 06:56

score 52 · Accepted Answer · answered Nov 09 '12 at 06:53

52

def initialize(opts={})
  opts.each { |k,v| instance_variable_set("@#{k}", v) }
end

answered Nov 09 '12 at 06:53

Casper

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Thanks, I just found this: http://stackoverflow.com/questions/9597249/in-ruby-can-i-automatically-populate-instance-variables-somehow-in-the-initializ/10855962 which is exactly what you are also saying. I will close my question as a duplicate, but upvote your answer. – mydoghasworms Nov 09 '12 at 06:56
4

Whitelisting the keys would be a good addition, a couple seconds to set up the whitelist now could save hours of debugging time later and help document the interface as a side effect. – mu is too short Nov 09 '12 at 07:31

score 4 · Answer 2 · answered Nov 09 '12 at 06:55

4

This should give you what you're looking for:

def initialize(opts={})
  opts.each_pair do |key, value|
    send("#{key}=",value)
  end
end

answered Nov 09 '12 at 06:55

brentmc79

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1

This only works if you have `setter` methods via `attr_accessor`, `attr_writer`, or manually created `setter` methods – ptierno Oct 07 '15 at 20:31

score 1 · Answer 3 · edited Apr 27 '16 at 03:34

1

you can do this with,

 @host, @user, @password, @project  = opts[:host], opts[:user], opts[:password], opts[:project]

hope this helps!

edited Apr 27 '16 at 03:34

cweston

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answered Nov 09 '12 at 06:57

maximus ツ

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J-_-L · Answer 4 · 2019-11-11T14:33:43.453

1

Besides Casper's solution, you could also use the instance_variables_from gem:

instance_variables_from(opts)

edited Nov 11 '19 at 14:33

answered Nov 09 '12 at 07:19

J-_-L

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Quickly setting instance variables with options hash in Ruby?

4 Answers4