notaion: Hash[*array_variable.flatten]

Can someone explain what the “*” operator inside the hash is doing here or what that notation is referred to in this context ? thanks

irb(main):006:0* mail_config

=> {“server_setings”=>{“address”=>“”, “port”=>25}}

irb(main):019:0> Hash[*mail_config[‘server_setings’].map { |k, v| [k.to_sym, v.t o_s] }.flatten]

=> {:address=>“”, :port=>“25”}

Try ...

def test(arg1, arg2=nil, arg3=nil, arg4=nil)   p arg1   p arg2   p arg3   p arg4 end

# Without the splat test(mail_config['server_setings'].map { |k, v| [k.to_sym, v.to_s] }.flatten) # [:address, "", :port, "25"] # nil # nil # nil

# With the splat test(*mail_config['server_setings'].map { |k, v| [k.to_sym, v.to_s] }.flatten) # :address # "" # :port # "25"

So, the splat operator explodes an array into the arguments of the method. First case without the splat you can see that the whole Array goes into the arg1. Second, with the splat, each arg gets one of the Array elements.

At your context the splat makes the call to Hash compatible with the form Hash[key1, value1, key2, value2, key3, value3, ...]

One thing to note is: Hash[*mail_config['server_setings'].map { |k, v| [k.to_sym, v.to_s] }.flatten] Hash[mail_config['server_setings'].map { |k, v| [k.to_sym, v.to_s] }] # Without the splat and without flatten are equivalents (for the given example). # And you can do it differently in a way that I think is more intuitive (for my taste).

mail_config['server_setings'].each_with_object({}) { |(k, v), hsh| hsh[k.to_sym] = v.to_s }

What do you think?

Hope it helped you, Abinoam Jr.