struct NoReturn
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") # => StringThe 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.crConstructors
Instance Method Summary
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