8 Statements [stmt.stmt]

8.7 Jump statements [stmt.jump]

8.7.5 The co_return statement [stmt.return.coroutine]

coroutine-return-statement:
co_return expr-or-braced-init-list

_{o p t}

;

A coroutine returns to its caller or resumer ([dcl.fct.def.coroutine]) by the co_return statement or when suspended ([expr.await]).

A coroutine shall not enclose a return statement ([stmt.return]).

[Note 1:

For this determination, it is irrelevant whether the return statement is enclosed by a discarded statement ([stmt.if]).

— end note]

The expr-or-braced-init-list of a co_return statement is called its operand.

Let p be an lvalue naming the coroutine promise object ([dcl.fct.def.coroutine]).

A co_return statement is equivalent to:

{ S; goto final-suspend; }

where final-suspend is the exposition-only label defined in [dcl.fct.def.coroutine] and S is defined as follows:

(2.1)
If the operand is a braced-init-list or an expression of non-void type, S is p.return_value(expr-or-braced-init-list).

The expression S shall be a prvalue of type void.
(2.2)
Otherwise, S is the compound-statement { expression $_{o p t}$ ; p.return_void(); }.

The expression p.return_void() shall be a prvalue of type void.

If p.return_void() is a valid expression, flowing off the end of a coroutine's function-body is equivalent to a co_return with no operand; otherwise flowing off the end of a coroutine's function-body results in undefined behavior.