void adjust_pos_or_size(const x::optional_args<optional_coords, optional_size> &args) { const std::optional<optional_coords> &c=x::optional_arg<optional_coords>(args); const std::optional<optional_coords> &c=x::optional_arg<optional_size>(args);
The x::optional_arg template retrieves
(a reference to) the
specified std::optional value. It's analogous
to std::get for std::tuples.
The optional value indicates whether this value was passed to
x::optional_args's constructor.
const auto &c=x::optional_arg<0>(args);
Similar to std::get,
x::optional_arg's type parameter works only
when the type is a unique x::optional_args
template parameter.
Like std::get,
a constant numerical x::optional_arg
template parameter specifies an
x::optional_args type by its 0-based index,
and this works when the same
type appears two or more times.
Two or more consecutive instances of the same type as
x::optional_args have the following results:
None of the option values, for this type, get set if the
corresponding values get passed to
x::optional_args's constructor.
The first value of the same type (or which can be implicitly converted to the type) initializes the first optional value of this type.
The next, immediately following, constructor parameter value initializes the next optional value of this type, and so on.
Effectively, the parameter values to the constructor initialize the corresponding optional values on a first come-first serve basis.
If any parameter values are left, after initializing all optional value, the program is ill-formed.