Ref. WGR Chapter 9, Section 9.3, Hashes
states = Hash.new
states["CA"] = "California"
states["MA"] = "Massachusetts"
states["NY"] = "New York"
states["MA"].reverse #=> "sttesuhcassaM"
a Hash can be defined literally (inline) with braces e.g.
states = {
"CA" => "California",
"MA" => "Massachusetts",
"NY" => "New York"
}
states["MA"] #=> "Massachusetts"
The little => arrow is called a hash rocket.
states = {:MA => "Massachusets"}
states["MA"] #=> nil
states[:MA] #=> "Massachusets"
This is such an annoying problem that Rails invented a new version of Hash named HashWithIndifferentAccess
that converts string keys into symbol keys.
(HashWithIndifferentAccess is such an annoying name that many people call it Mash instead.)
Ruby 1.8 or 1.9:
{:foo => "bar", :baz => "baf"}
Ruby 1.9 only:
{foo: "bar", baz: "baf"}
When passing a hash to a method,
the braces are optional...
...**if** you're calling a method
...**and** the hash is the final argument
invite({:name => "Alice", :age => 18})
invite :name => "Alice", :age => 18
This is called "the default hash" (which is a silly name for it).
These are all equivalent:
User.new({:name => "Alex", :email => "alex@stinky.com"})
User.new(:name => "Alex", :email => "alex@stinky.com")
User.new :name => "Alex", :email => "alex@stinky.com"
User.new name: "Alex", email: "alex@stinky.com"
User.new email:"alex@stinky.com", name:"Alex"
...so passing a hash literal kinda sorta almost looks like named parameters.
(Ruby 2.0 will support proper named parameters, using the same calling syntax.)
merge to combine two hashesHere's a handy trick:
class Hash
alias_method :<<, :merge!
alias_method :+, :merge
end
{foo: 1} << {bar: 2}
=> {:foo=>1, :bar=>2} # destructive
{foo: 1} + {bar: 2}
=> {:foo=>1, :bar=>2} # constructive
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