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T.noreturn

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T.noreturn

This indicates that a method never returns. Some examples of things that never return are: infinite loops, exiting the program, and raising exceptions.

This powers dead code analysis. If you try to do something with a value of type T.noreturn, you will get an unreachable code error.

# typed: true
extend T::Sig

sig {returns(T.noreturn)}
def loop_forever
  loop {}
end

sig {returns(T.noreturn)}
def exit_program
  exit
end

sig {returns(T.noreturn)}
def raise_always
  raise RuntimeError
end

x = exit_program
puts x # error: This code is unreachable

T.noreturn is a subtype of every type, but no type except T.noreturn (trivially) and T.untyped is a subtype of T.noreturn.