What does map(&:name) mean in Ruby?

Question

I found this code in a RailsCast:

def tag_names
  @tag_names || tags.map(&:name).join(\' \')
end

What does the (&:name)

Answer 1

(&:name) is short for (&:name.to_proc) it is same as tags.map{ |t| t.name }.join(' ')

to_proc is actually implemented in C

Answer 2

tags.map(&:name)

is The same as

tags.map{|tag| tag.name}

&:name just uses the symbol as the method name to be called.

Answer 3

First, &:name is a shortcut for &:name.to_proc, where :name.to_proc returns a Proc (something that is similar, but not identical to a lambda) that when called with an object as (first) argument, calls the name method on that object.

Second, while & in def foo(&block) ... end converts a block passed to foo to a Proc, it does the opposite when applied to a Proc.

Thus, &:name.to_proc is a block that takes an object as argument and calls the name method on it, i. e. { |o| o.name }.

Answer 4

It's shorthand for tags.map { |tag| tag.name }.join(' ')

Answer 5

Here :name is the symbol which point to the method name of tag object. When we pass &:name to map, it will treat name as a proc object. For short, tags.map(&:name) acts as:

tags.map do |tag|
  tag.name
end

Answer 6

It is same as below:

def tag_names
  if @tag_names
    @tag_names
  else
    tags.map{ |t| t.name }.join(' ')
end