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While learning Ruby I've come across the "=>" operator on occasion. Usually I see it in the form of
:symbol => value
and it seems to be used frequently when passing values to functions. What exactly is that operator called? What does it do/mean? Is it built into Ruby or is it something that different frameworks like Rails and DataMapper add to the symbol class? Is it only used in conjunction with the symbol class? Thanks.
=>
separates the keys from the values in a hashmap literal. It is not overloadable and not specifically connected to symbols.
A hashmap literal has the form {key1 => value1, key2 => value2, ...}
, but when used as the last parameter of a function, you can leave off the curly braces. So when you see a function call like f(:a => 1, :b => 2)
, f
is called with one argument, which is a hashmap that has the keys :a
and :b
and the values 1
and 2
.
You might hear this operator referred to as a "hash rocket," meaning you use it when defining a ruby hash.
This is the Ruby Hash documentation, if you're not familiar: http://www.ruby-doc.org/core/classes/Hash.html
Note that in Ruby 1.9, if you're defining a hash that uses symbols as keys, there's now an alternative syntax available to you: http://blog.peepcode.com/tutorials/2011/rip-ruby-hash-rocket-syntax
Tip: if you're using it in a hash like {:a => "A", :b => "B"}
, in Ruby 1.9, you can use it like a JSON hash:
{
a: "A",
b: "B"
}
If you want to do any further Googling, =>
is sometimes called a hashrocket, because it looks like a rocket (in the same sense that <=>
looks like a spaceship), and it's used in hashes.
Or you could use SymbolHound.
In addition to In Ruby what does "=>" mean and how does it work?:
You mostly will see the =>
to define parameters for a function. Think of this as a nice convenience: You need not remember the right order of your parameters, as all parameters are wrapped into a giant hash. So if you have a simple helper method like
link_to "My link", my_path, :confirm => "Are you sure?"
this is way better than
link_to "My link", my_path, null, null, null, null, "Are you sure?"
just because you want to use a rarely used parameter. So passing parameters with a hash is just a convention in Ruby/Rails to make life easier.
来源:https://stackoverflow.com/questions/4663074/in-ruby-what-does-mean-and-how-does-it-work