# struct NoReturn

- NoReturn
- Struct
- Value
- Object

##
Overview

Some expressions won't return to the current scope and therefore have no return type. This is expressed as the special return type `NoReturn`.

Typical examples for non-returning methods and keywords are `return`, `exit`, `raise`, `next`, and `break`.

This is for example useful for deconstructing union types:

    string = STDIN.gets
    typeof(string)                        # => String?
    typeof(raise "Empty input")           # => NoReturn
    typeof(string || raise "Empty input") # => String

The compiler recognizes that in case string is Nil, the right hand side of the expression `string || raise` will be evaluated. Since `typeof(raise "Empty input")` is `NoReturn` the execution would not return to the current scope in that case. That leaves only `String` as resulting type of the expression.

Every expression whose code paths all result in `NoReturn` will be `NoReturn` as well. `NoReturn` does not show up in a union type because it would essentially be included in every expression's type. It is only used when an expression will never return to the current scope.

`NoReturn` can be explicitly set as return type of a method or function definition but will usually be inferred by the compiler.

NOTE This is a pseudo-class provided directly by the Crystal compiler. It cannot be reopened nor overridden.

##
Defined in:

docs_pseudo_methods.cr

##
Constructors

- .new

##
Instance Method Summary

- #initialize

### Instance methods inherited from struct `Struct`

==(other) : Bool ==, hash(hasher) hash, inspect(io : IO) : Nil inspect, pretty_print(pp) : Nil pretty_print, to_s(io : IO) : Nil to_s

### Instance methods inherited from struct `Value`

==(other : JSON::Any)
==(other : YAML::Any)
==(other) ==, dup dup

### Instance methods inherited from class `Object`

! : Bool !, !=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other) ===, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash(hasher)
hash hash, in?(collection : Object) : Bool
in?(*values : Object) : Bool in?, inspect(io : IO) : Nil
inspect : String inspect, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil!(message)
not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) tap, to_json(io : IO) : Nil
to_json : String to_json, to_pretty_json(indent : String = " ") : String
to_pretty_json(io : IO, indent : String = " ") : Nil to_pretty_json, to_s(io : IO) : Nil
to_s : String to_s, to_yaml(io : IO) : Nil
to_yaml : String to_yaml, try(&) try, unsafe_as(type : T.class) forall T unsafe_as

### Class methods inherited from class `Object`

from_json(string_or_io, root : String)
from_json(string_or_io) from_json, from_yaml(string_or_io : String | IO) from_yaml

### Macros inherited from class `Object`

class_getter(*names, &block) class_getter, class_getter!(*names) class_getter!, class_getter?(*names, &block) class_getter?, class_property(*names, &block) class_property, class_property!(*names) class_property!, class_property?(*names, &block) class_property?, class_setter(*names) class_setter, def_clone def_clone, def_equals(*fields) def_equals, def_equals_and_hash(*fields) def_equals_and_hash, def_hash(*fields) def_hash, delegate(*methods, to object) delegate, forward_missing_to(delegate) forward_missing_to, getter(*names, &block) getter, getter!(*names) getter!, getter?(*names, &block) getter?, property(*names, &block) property, property!(*names) property!, property?(*names, &block) property?, setter(*names) setter

##
Constructor Detail

def self.new #

##
Instance Method Detail

def initialize #