Function Optional.opAssign
Assigns a value to the optional or sets it to none.
ref auto opAssign
(
const None
);
ref auto opAssign(U)
(
auto ref U lhs
)
if (isMutable!T && isAssignable!(T, U));
ref auto opAssign(U)
(
auto ref Optional!U lhs
)
if (isMutable!T && isAssignable!(T, U));
If T is of class type, interface type, or some function pointer than passing in null
sets the optional to none internally