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:
to_con.crConstructors
Instance Method Summary
Instance methods inherited from struct Value
==(other : CON::Any)
==
Instance methods inherited from class Object
===(other : CON::Any)
===,
from_con(con : String | IO)
from_con,
to_con(io : IO)to_con to_con, to_pretty_con(indent : String = " ")
to_pretty_con(io : IO, indent : String = " ") to_pretty_con