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Thanh’s Notes

The colon in Ruby is quite confusing

·2 mins

The position of the colon in Ruby code confused me for a few days.

1. Before a text (:foo) #

:hello

In route definition

redirect_to :action => "edit", :id => params[:id]

redirect_to method

In the view

  <%= link_to "Delete", article, confirm: "Are you sure?", method: :delete %>

The method: :delete is quite confusing. It’s actually {method: :delete}

:delete is not change in the application. so we can use :symbol here. But why not use constant?

symbols are values, constants are not. (Constants are references to values). Symbols evaluate to themselves, constants evaluate to whatever value they reference.

From: https://stackoverflow.com/questions/47047954/are-ruby-symbols-the-equivalent-of-php-constants

Check the API docs of link_to method

def link_to(name = nil, options = nil, html_options = nil, &block)
  html_options, options, name = options, name, block if block_given?
  options ||= {}

  html_options = convert_options_to_data_attributes(options, html_options)

  url = url_for(options)
  html_options["href"] ||= url

  content_tag("a", name || url, html_options, &block)
end

so the confirm and method is the html_options

This method accepts 2 params

  • action
  • id

2. After (foo:) #

Keyword arguments #

hello:

def calculate_total(subtotal:, tax:, discount:)
  subtotal + tax - discount
end

subtotal, tax, discount are required and allow switch order of arguments.

calculate_total(subtotal: 100, discount: 5, tax: 10)

Hash key #

if we want a string is a hash key then must arrow/rocket syntax

# this will work
my_hash = {
  "cool" => :thing
}
#=> {"cool" => :thing }

# this will not work
my_hash = {
  "cool": :thing
}
#=> { :cool => :thing }
# converts the string "cool" to a symbol

# in a hash:
my_hash = {
  :cool => :symbol
}
# is the same as...
my_hash = {
  cool: :symbol
}

Reference:

3. Double colon #

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