Sending elements of an array as arguments to a method call

Question

I have a method that accepts the splat operator:

def hello(foo, *bar)   
   #... do some stuff 
end

I have an array with a variable length that I'd like to send into this hello method:

arr1 = ['baz', 'stuff']
arr2 = ['ding', 'dong', 'dang']

I'd like to call the method with arr1 and arr2 as arguments to that method but I keep getting hung up in that *bar is being interpreted as an array instead of individual arguments. To make things more fun, I can't change the hello method at all.

I'm looking for something similar to this SO question but in ruby.

Please accept correct answers to your questions by clicking inside the hollow checkmark to the left of the most helpful answer. Thanks! :) — Jacob Relkin
– Jacob Relkin, Commented Dec 29, 2010 at 11:10

Ivan Castellanos · Accepted Answer · 2017-09-22 21:49:56Z

15

try calling it like this

hello(arr1, *arr2)

here's a run through in irb

irb(main):002:0> def hello(foo, *bar)
irb(main):003:1>   puts foo.inspect
irb(main):004:1>   puts bar.inspect
irb(main):005:1> end
=> nil
irb(main):006:0> arr1 = ['baz', 'stuff']
=> ["baz", "stuff"]
irb(main):007:0> arr2 = ['ding', 'dong', 'dang']
=> ["ding", "dong", "dang"]
irb(main):008:0> hello(arr1, arr2)
["baz", "stuff"]
[["ding", "dong", "dang"]]
=> nil
irb(main):009:0> hello(arr1, *arr2)
["baz", "stuff"]
["ding", "dong", "dang"]
=> nil

by adding the * to the second array, it treats them as an array instead of an array of an array, which is what you're looking for i think

edited Sep 22, 2017 at 21:49

Ivan Castellanos

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answered Dec 29, 2010 at 8:40

mportiz08

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1 Comment

brycemcd Over a year ago

thanks, that's exactly what was happening. Even when I called bar.class on the passed in arguments, I was seeing array. I didn't think it could be an array of an array.

Jacob Relkin · Accepted Answer · 2010-12-29 09:15:40Z

10

Here you go:

hello('Something', *(arr1 + arr2))

This will combine the arr1 and arr2 arrays and collectively pass them from the second argument on to the method.

Example:

>> def hello(str, *args)
>> puts str
>> args.each do |arg|
?>   puts 'Splat: ' + arg
>> end
>> end
=> nil
>> hello('Hello', *(['programming'] + ['is', 'fun']))
Hello
Splat: programming
Splat: is
Splat: fun
=> ["programming", "is", "fun"]

The last parameter of a method may be preceded by an asterisk(*), this indicates that more parameters may be passed to the function. Those parameters are collected up and an array is created.

Since the last parameters are collected up into an array, you need to use the * operator to indicate that you are indeed sending an array to the method and that it shouldn't wrap the arguments in another array.

edited Dec 29, 2010 at 9:15

answered Dec 29, 2010 at 8:42

Jacob Relkin

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4 Comments

Mladen Jablanović Over a year ago

Any reason you prefer pasting screenshots instead of actual code?

Jacob Relkin Over a year ago

@Mladen Jablanovic No reason at all, in fact if you prefer I will paste in the code.

Mladen Jablanović Over a year ago

Thanks. I guess it's just matter of time when someone will actually print the code, scan the printed paper and attach it as an image. :)

brycemcd Over a year ago

This is also spot on, but I'm looking to pass in the arrays as separate method calls. I ranked the answer up.

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