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.cr

Constructors

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

Constructor Detail

def self.from_con(pull : CON::PullParser) : Nil #

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Instance Method Detail

def to_con(con : CON::Builder) #

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