I am trying to figure out what &:hex mean in this code
sort_by{|x|x.scan(/\d*/).map &:hex}
The full code looks like this
class Array
def version_sort
sort_by{|x|x.scan(/\d*/).map &:hex}
end
end
I know that map does an action to the scanned part , so I am guessing it replaces numbers
(/\d*/)
with
&:hex
but I dont know what that means
In this case & takes an object and if the object is not already a Proc, as it is the case with the Symbol :hex it will try to invoke the method to_proc on it. In the Symbol documentation you will find the implementation detail for the to_proc method:
to_proc
Returns a Proc object which respond to the given method by sym.
(1..3).collect(&:to_s) #=> ["1", "2", "3"]
In your case through &:hex the symbol :hex will be converted into the Proc object which is equivalent to { |item| item.hex() }
What is a Proc exactly? Basically the Proc class is a basic anonymous function. In Ruby the notion of a callable object is embodied in Ruby through objects to which you can send the message call. The main representatives of these kind are Proc and Lambda.
Proc objects are self-contained code sequences, that can be created, stored, passed around as method arguments and executed at some point through call. A method like map can also take a block as an argument which is the case if you pass &:hex.
In the method definition of map a kind of implicit call to Proc.new is made using the very same block. Then the Proc is executed through its call method executing the code embodied by the Proc object.
These two expressions are equivalent:
foo.map {|x| x.hex}
foo.map &:hex
