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 my findings.
- Generally used in “Method definition with variable no. of parameter”.
def demo(*numbers)
numbers.each { |num| puts "#{num}" }
end
demo(1,2,3,4)
#output
1
2
3
4
- 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
- Use in
casestatement :
male = ["ram", "rahul", "karan"]
female = ["kareena", "aish", "juhi", "katerina"]
person = "aish"
case person
when *male
puts "Male"
when *female
puts "Female"
end
#output
Female
- 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"
- Datatype Coercion : Splat operator can be used to convert interesting datatype coercion.
a) 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.
b) 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
c) Hash into an Array:
arr = *{ :a => "111", :b => "222" } # [[:a, "111"], [:b, "222"]]
Note : Use Hash[*arr.flatten] to reverse it.
