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Blocks, Procs, and Lambdas

Proc Syntax

Procs are easy to define! You just call and pass in the block you want to save. Here's how we'd create a proc called cube that cubes a number (raises it to the third power):

cube = { |x| x ** 3 }

We can then pass the proc to a method that would otherwise take a block, and we don't have to rewrite the block over and over!

[1, 2, 3].collect!(&cube) # ==> [1, 8, 27] [4, 5, 6].map!(&cube) # ==> [64, 125, 216]

(The .collect! and .map! methods do the exact same thing.)

The & is used to convert the cube proc into a block (since .collect! and .map! normally take a block). We'll do this any time we pass a proc to a method that expects a block.

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