Intro to Splat (*) operator in Ruby.

I usually use following to create a bunch of array elements in Ruby.

arr = (10..50).to_a     #converting a range to an array.

Today I noticed following which performs same operation:

arr = [*10..50]       # splat operator

My reaction was :
“Awesome!!!!”

So, then, one day I took some time to investigate more on this (*) operator.
Following are few which I could come to know.

1) Generally used in “Method definition with variable no. of parameter” (I have used it but don’t know it was implementation of splat operator (^o^) )

def demo(*numbers)
  numbers.each { |num| puts "#{num}" }
end
demo(1,2,3,4)

#output
1
2
3
4

2) Converting an array into list of arguments in method calling.
In this case, the splat converts the array into method arguments.

def demo(arg1, arg2, arg3)
  puts "arg1 is #{arg1}, arg2 is #{arg2} and arg3 is #{arg3}"
end
arr = [10, 20.45, "hello"]
demo *arr

#output
arg1 is 10, arg2 is 20.45 and arg3 is hello

3) Datatype coercion
Splat operator can be used to convert interesting datatype coercion.

3.1) String into Array : Splat can also be used to coerce string values into array.

arr = *"Hello"  #=> ["Hello"]
"Hello".to_a  #=> NoMethodError: undefined method `to_a' for "Hello":String

Note : This will only create array of size 1.

3.2) Range into Array :

arr = *(10..20)     # [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

Above is similar behavior as ‘arr = (10..20).to_a’

3.3) Hash into an Array:

arr = *{ :a => "111", :b => "222" }    # [[:a, "111"], [:b, "222"]]

Note : Use ‘Hash[*arr.flatten]’ to reverse it.

4) Use in ‘case’ statement :

male = ["ram", "rahul", "karan"]
female = ["kareena", "aish", "juhi", "katerina"]
person = "aish"

case person
when *male
  puts "Male"
when *female
  puts "Female"
end

#output
Female

5) Interesting Array data retrieval:

arr = ["one", "two", "three", "four"]

first, *others = arr         #first = "one", others = ["two", "three", "four"]
*others, last = arr          #others = ["one", "two", "three"] , last = "four"
first, *center, last = arr   #first = "one", center = ["two", "three"], last = "four"