struct Nil
inherits Value
¶
The Nil type has only one possible value: nil.
nil is commonly used to represent the absence of a value.
For example, String#index returns the position of the character or nil if it's not
in the string:
str = "Hello world"
str.index 'e' # => 1
str.index 'a' # => nil
In the above example, trying to invoke a method on the returned value will
give a compile time error unless both Int32 and Nil define that method:
str = "Hello world"
idx = str.index 'e'
idx + 1 # Error: undefined method '+' for Nil
The language and the standard library provide short, readable, easy ways to deal with nil,
such as Object#try and Object#not_nil!:
str = "Hello world"
# The index of 'e' in str or 0 if not found
idx1 = str.index('e') || 0
idx2 = str.index('a')
if idx2
# Compiles: idx2 can't be nil here
idx2 + 1
end
# Tell the compiler that we are sure the returned
# value is not nil: raises a runtime exception
# if our assumption doesn't hold.
idx3 = str.index('o').not_nil!
Class methods¶
Methods¶
#object_id
¶
Returns 0_u64. Even though Nil is not a Reference type, it is usually
mixed with them to form nilable types so it's useful to have an
object id for nil.
#presence
¶
Returns self.
This method enables to call the presence method (see String#presence) on a union with Nil.
The idea is to return nil when the value is nil or empty.
config = {"empty" => ""}
config["empty"]?.presence # => nil
config["missing"]?.presence # => nil