Creating a hash from an array - how does it work?

Question

fruit = ["apple","red","banana","yellow"] => ["apple", "red", "banana", "yellow"] Hash[*fruit] => {"apple"=>"red", "banana"=>"yellow"} 

Why does splat make an array so neatly understand Hash?

Or, more precisely, how does the hash “know” that “apple” is the key, and “red” is its corresponding value?

Is it simply because they are in consecutive positions in the fruit array?

Does splat use here? Can a hash not define itself from arry so directly differently?

Answer 1

As the documentation reports:

 Hash["a", 100, "b", 200] #=> {"a"=>100, "b"=>200} Hash["a" => 100, "b" => 200] #=> {"a"=>100, "b"=>200} { "a" => 100, "b" => 200 } #=> {"a"=>100, "b"=>200} 

You cannot pass an array to the Hash[] method according to the documentation, so splat is just a way to explode the fruit array and pass its elements as normal arguments to Hash[] . Indeed, this is a very common use of the splat operator.

The most interesting thing is that if you try to pass an odd number of Hash arguments, you will get an ArgumentError exception:

 fruit = ["apple","red","banana","yellow","orange"] #=> ["apple", "red", "banana", "yellow", "orange"] Hash[*fruit] #=> ArgumentError: odd number of arguments for Hash 

Answer 2

Look at the open class method [] in the Hash class. (Let's say here.) It clearly states that a new Hash (instance) will be created and populated with these objects. Naturally, they are found in pairs. The splat operator significantly expands the array when used as a parameter.