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? — mydoghasworms
– mydoghasworms, Commented Nov 9, 2012 at 6:56

Casper · Accepted Answer · 2012-11-09 06:53:29Z

52

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

answered Nov 9, 2012 at 6:53

Casper

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2 Comments

mydoghasworms Over a year ago

Thanks, I just found this: stackoverflow.com/questions/9597249/… which is exactly what you are also saying. I will close my question as a duplicate, but upvote your answer.

mu is too short Over a year ago

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.

brentmc79 · Accepted Answer · 2012-11-09 06:55:31Z

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 9, 2012 at 6:55

brentmc79

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1 Comment

ptierno Over a year ago

This only works if you have setter methods via attr_accessor, attr_writer, or manually created setter methods

cweston · Accepted Answer · 2016-04-27 03:34:40Z

1

you can do this with,

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

hope this helps!

edited Apr 27, 2016 at 3:34

cweston

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answered Nov 9, 2012 at 6:57

maximus ツ

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Comments

J-_-L · Accepted Answer · 2019-11-11 14:33:43Z

1

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

instance_variables_from(opts)

edited Nov 11, 2019 at 14:33

answered Nov 9, 2012 at 7:19

J-_-L

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