Procs & Closures

A Proc is a block you can store and pass around

A block isn't an object — you can't put it in a variable or return it. A Proc is: it's a block turned into a first-class object you can store, pass, and call later. This is Ruby's version of a function value / closure, and it's the substrate lambdas are built on.

greet = Proc.new { |name| "Hi #{name}" }
greet.call("Priya")   # "Hi Priya"
greet.("Priya")       # same thing, .() sugar
greet["Priya"]        # same thing, [] sugar

In an interview, say: "A Proc is a callable object that captures the block and the surrounding local variables — a closure. Blocks are the lightweight syntax; procs are blocks promoted to objects."