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

There's no magic, symbol (method) is just one of the possible parameters. This is from the docs:

  # enum.inject(initial, sym) => obj
  # enum.inject(sym)          => obj
  # enum.inject(initial) {| memo, obj | block }  => obj
  # enum.inject          {| memo, obj | block }  => obj

Ours case is the second one.

You can also rewrite it with traditional block:

op = :+   #  parameter of inject call
[1,2,3,4,5,6,7].inject {|sum, x| sum.send(op, x)} #  also returns 28

(to answer "how does it work" part)