One pretty well-know idiom in Ruby, and Facets, is Symbol.to_proc . It lets you turn these:

[1, 2, 3].map { |num| num.next } #=> [2, 3, 4] %w[alpha beta gamma].map { |word| word.upcase } #=> ["ALPHA", "BETA", "GAMMA"]

…into these:

[1, 2, 3].map(&:next) %w[alpha beta gamma].map(&:upcase)

It’s a nice little trick, though it’s not to everyone’s taste. If you’re already comfortable with Symbol.to_proc , you can skip down to the Class.to_proc section. But if you’re not, it’s worth a minute of your attention to learn it. Read on…

How it’s done

When a method takes a block, you can call yield, to run the block.

def with_a_block(a_param) yield end with_a_block('param') { puts 'in the block' }

Or, you can name the block as the last parameter to the method, and put an ampersand in front of it. The ampersand makes ruby convert the block to a procedure, by calling to_proc on it. (So any object with a to_proc method can work this way, if you want.) This example works just like the last one:

def named_block(a_param, &blk) blk.call end named_block('my_param') { puts 'in the named block' }

Symbol’s to_proc method creates a procedure that takes one argument, and sends the symbol to it. Sending a symbol to an object is the same as calling a method on it: object.send(:method) works the same as object.method . In the earlier upcase example, each word is passed to a procedure that calls upcase on it, giving us a list of uppercased strings.

&:upcase # becomes... lambda { |obj| obj.send(:upcase) } # or... lambda { |obj| obj.upcase }

Class.to_proc

So Symbol.to_proc creates a function that takes an argument, and calls that method on it. Class.to_proc creates a function that passes its argument to its constructor, yielding an instance of itself. This is a welcome addition to the to_proc family.

require 'facets' class Person def initialize(name) @name = name end end names = %w[mickey minney goofy] characters = names.map(&Person) puts characters.inspect &Person # becomes... lambda { |obj| Person.new(obj) }

Why it’s nice

It’s fewer characters — it semantically compresses your code.

It lets you think, makes you think, on a higher level. You think about operations on your data, rather than handling one item at a time. It raises your level of thinking.

you think, on a higher level. You think about operations on your data, rather than handling one item at a time. It raises your level of thinking. It works with first-class functions, which are worth understanding. They give you new ways to elegantly solve some problems (well, new to some audiences). They’re not fringe anymore — they’ve been in C# since v2.0.