I'm confused by Ruby notation [duplicate] - ruby

Question

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Is there any difference between the `:key => "value"` and `key: "value"` hash notations?
(5 answers)
Closed 5 years ago.
When using Ruby, I keep getting mixed up with the :.
Can someone please explain when I'm supposed to use it before the variable name, like :name, and when I'm supposed to use it after the variable like name:?
An example would be sublime.

Answer 1

This has absolutely nothing to do with variables.
:foo is a Symbol literal, just like 'foo' is a String literal and 42 is an Integer literal.
foo: is used in three places:
as an alternative syntax for Symbol literals as the key of a Hash literal: { foo: 42 } # the same as { :foo => 42 }
in a parameter list for declaring a keyword parameter: def foo(bar:) end
in an argument list for passing a keyword argument: foo(bar: 42)

Answer 2

You are welcome for both, while creating Hash :
{:name => "foo"}
#or
{name: 'foo'} # This is allowed since Ruby 1.9
But basically :name is a Symbol object in Ruby.
From docs
Hashes allow an alternate syntax form when your keys are always symbols. Instead of
options = { :font_size => 10, :font_family => "Arial" }
You could write it as:
options = { font_size: 10, font_family: "Arial" }

Answer 3

:name is a symbol. name: "Bob" is a special short-hand syntax for defining a Hash with the symbol :name a key and the string "Bob" as a value, which would otherwise be written as { :name => "Bob" }.

Answer 4

You can use it after when you are creating a hash.
You use it before when you are wanting to reference a symbol.
In Arup's example, {name: 'foo'} you are creating a symbol, and using it as a key.
Later, if that hash is stored in a variable baz, you can reference the created key as a symbol:
baz[:name]