Question

I’m going through Beginning Ruby From Novice To Professional 2nd Edition and am currently on page 49 where we are learning about RegEx basics. Each RegEx snippet in the book has a code trailing it that hasn’t been explained.

{ |x| puts x }

In context:

"This is a test".scan(/[a-m]/) { |x| puts x }

Could someone please clue me in?

Answer 1

A method such as scan is an iterator; in this case, each time the passed regex is matched, scan does something programmer-specified. In Ruby, the “something” is expressed as a block, represented by { code } or do code end (with different precedences), which is passed as a special parameter to the method. A block may start with a list of parameters (and local variables), which is the |x| part; scan invokes the block with the string it matched, which is bound to x inside the block. (This syntax comes from Smalltalk.)

So, in this case, scan will invoke its block parameter every time /[a-m]/ matches, which means on every character in the string between a and m.