How does this ruby injection magic work?

Question

I saw a ruby code snippet today.

[1,2,3,4,5,6,7].inject(:+)  

=> 28

[1,2,3,4,5,6,7].inject(:*)  
         


        

Answer 1

The :+ is a symbol representing the addition message. Remember that Ruby has a Smalltalk style where just about every operation is performed by sending a message to an object.

As discussed in great detail here, (1..100).inject(&:+) is valid syntax in earlier versions where Rails has added the to_proc extension to Symbol.

The ability to pass just a symbol into inject was new in 1.9 and backported into 1.8.7.