Methods

Signatures

Method signatures can be defined with a selection of different argument styles.

Optional arguments

Here we can assign default values that will be used if none is passed.

def method(optional = "optional")
    ...
end

Type Matching/Overloading

You can define the same method multiple times with different argument types, and have them behave differently.

def method(item : Int32)
    ...
end

def method(item : String)
    ...
end

Splat argument

This argument takes a list of items rather than a single one. The items eventually are resolved to tuples.

def method(*items)
    ...
end

Named arguments

def method(nameOne argumentOne, nameTwo argumentTwo)
    ...
end

method nameOne: "some string", nameTwo: 12345

Double splats

Double splat arguments allow you to pass a list of arguments in the format of key: value

def method(**arguments)
    ...
end

method argumentOne: valueOne, argumentTwo: valueTwo

Scope

Methods and classes are public by default. For both, you can limit the scope by adding the private or protected keyword in front of the def or class keyword.

Return types

Method return types are always inferred, but you can specify the return type of a method by doing the following:

def method(argumentOne, argumentTwo) : Number
    ...
end

The method defined above will return a Number. A type restriction can either be a type or self, which refers to the current class.

If you specify that a method has a return type of Nil, then Crystal will always return nil for that method.