struct Nil
Overview
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!
Defined in:
crystal_on_steroids/nil.crcrystal_on_steroids/to_query.cr
Instance Method Summary
Instance methods inherited from class Object
in?(another_object)
in?,
presence
presence,
presence_in(another_object)
presence_in,
present?
present?,
to_param
to_param,
to_query(namespace)to_query to_query