Nil
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:
nil.crjson/to_json.cr
yaml/to_yaml.cr
Class Method Summary
Instance Method Summary
- #==(other : Nil)
Returns
true
:Nil
has only one singleton value:nil
- - #clone
- #hash
Returns
0
. - #inspect(io)
Writes
"nil"
to the givenIO
- - #inspect
Returns
"nil"
. - #not_nil!
Raises an exception.
- #object_id
Returns
0_u64
. - #same?(other : Nil)
Returns
true
:Nil
has only one singleton value:nil
- - #same?(other : Reference)
Returns
false
. - #to_json(json : JSON::Builder)
- #to_s(io : IO)
Doesn't write anything to the given
IO
- - #to_s
Returns an empty string.
- #to_yaml(yaml : YAML::Builder)
- #try(&block)
Doesn't yields to the block.
Instance methods inherited from struct Value
==(other) ==, dup dup Instance methods inherited from class Object
!=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)===(other : YAML::Any)
===(other) ===, =~(other) =~, class class, dup dup, hash hash, inspect(io : IO)
inspect inspect, itself itself, not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, tap(&block) tap, to_json(io : IO)
to_json to_json, to_pretty_json(indent : String = " ")
to_pretty_json(io : IO, indent : String = " ") to_pretty_json, to_s
to_s(io : IO) to_s, to_yaml(io : IO)
to_yaml to_yaml, try(&block) try
Class methods inherited from class Object
from_json(string_or_io, root : String) : selffrom_json(string_or_io) : self from_json, from_yaml(string_or_io) : self from_yaml
Class Method Detail
def self.new(pull : JSON::PullParser)Source
def self.new(pull : YAML::PullParser)Source
Instance Method Detail
def cloneSource
def hashSource
Returns 0
.
def inspectSource
Returns "nil"
.
def not_nil!Source
Raises an exception.
See also: Object#not_nil!
.
def object_idSource
def to_json(json : JSON::Builder)Source
def to_sSource
Returns an empty string.
def to_yaml(yaml : YAML::Builder)Source
def try(&block)Source
Doesn't yields to the block.
See also: Object#try
.
© 2012–2017 Manas Technology Solutions.
Licensed under the Apache License, Version 2.0.
https://crystal-lang.org/api/0.22.0/Nil.html