Using Ruby hash key as parameters

Question

I am trying to use a parameter as my key to find the value in a hash, and I just confused about why I couldn't get the value by the first way. I am new to Ruby.

def getCards(player,hash)
    a =$player
    puts "a = "+a.to_s
    puts "a.class = "+a.class.to_s

    puts " hash[:a]"+" #{hash[:a]}"
    puts " hash[:'1']"+" #{hash[:"1"]}"

 end

edit:

 def getCards(player,hash)
   puts player 
  #result successfully 1 or any number that I gets from console

   puts hash[player]
   # nothing but 1 is actually a key in my hash 

# {1=>["yellow3", "yellow8", "green9", "black11", "red1", "black7", "red5", #"yellow7",  more results ..

 end

hash["1"] returns a result that I need , however why I can not use a variable as a parameter key to get the value? — Yang Liu
– Yang Liu, Commented Oct 9, 2017 at 15:08

tadman · Accepted Answer · 2017-10-09 02:03:40Z

3

Note that Ruby is not PHP or Perl, so that should be player and not $player. Argument names and their corresponding use as variables are identical.

$player refers to the global variable of that name, which is unrelated and will be presumed to be undefined unless otherwise set.

Now if by hash[:a] you mean to access the contents of the hash under the key with the player value you've assigned to a then what you actually want is:

hash[player]

Where that represents looking up an entry with that key. a is a variable in this case, :a is the symbol "a" which is just a constant, like a label, which has no relation to the variable.

Don't forget that "#{x}" is equivalent to x.to_s so just use interpolation instead of this awkward "..." + x.to_s concatenation.

Another thing to keep in mind is that in Ruby case has significant meaning. Variable and method names should follow the get_cards style. Classes are ClassName and constants are like CONSTANT_NAME.

answered Oct 9, 2017 at 2:03

tadman

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6 Comments

Yang Liu Over a year ago

thanks for your answer, but why I can not assign a =$player?

tadman Over a year ago

You can do that, but it doesn't mean anything here since $player is nil and completely unrelated to the player argument. Just because it's valid Ruby code doesn't mean it works as you expect.

Yang Liu Over a year ago

def getCards(player,hash) puts player // result 1 puts hash[player] result nil end

Yang Liu Over a year ago

I gave player = 1 , and puts 1 successfully ,buy why hash[player] returns nil? and player.class = string

Yang Liu Over a year ago

Thanks tadman , I solved the problem by changed the type of my key ,I used int as my key and it works fine by puts hash[players.to_i] and player is a parameter that was sent previously .

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