Blocks and yield in Ruby

I’ve found that the simplest way to think about blocks is as functions that you can pass to methods for execution later.

yield calls a block passed implicitly with the do ... end or curly brace syntax. Any arguments passed to yield are passed to the block. You also pass a block explicitly to a method with an ampersand parameter, which allows you to then call that block. Passing a block like this converts it to a proc.

Procs and lambdas are like blocks, but they can be stored in variables. Both retain the scope within which they were defined (they are closures). Procs and lambdas behave slightly differently: return in a proc will return from the calling method, whereas a lambda will just return from itself; lambdas enforce arguments, whereas procs do not.

A good reference: https://blog.appsignal.com/2018/09/04/ruby-magic-closures-in-ruby-blocks-procs-and-lambdas.html