All lambdas passed to test_using_reusable_sst() conform to the prototype
void (test_env&, sstable_ptr)
All lambdas passed to test_using_reusable_sst_returning() conform to the
prototype
NON_VOID (test_env&, sstable_ptr)
The common parameter list of both prototypes can be expressed with the
concept
std::invocable<test_env&, sstable_ptr>
Once a "Func" template parameter (i.e., function type) satisfying this
concept is taken, then "Func"'s void or non-void return type can be
commonly expressed with
std::invoke_result_t<Func, test_env&, sstable_ptr>
In turn, test_env::do_with_async_returning<...> can be instantiated with
this return type, even if it happens to be "void".
([stmt.return] specifies, "[a] return statement with an operand of type
void shall be used only in a function that has a cv void return type",
meaning that
return func(env)
will do the right thing in the body of
test_env::do_with_async_returning<void>().)
Merge test_using_reusable_sst() and test_using_reusable_sst_returning()
into one. Preserve the function name from the former, and the
test_env::do_with_async_returning<...>() call from the latter.
Suggested-by: Avi Kivity <avi@scylladb.com>
Signed-off-by: Laszlo Ersek <laszlo.ersek@scylladb.com>
Closesscylladb/scylladb#20090
607abe96e8