struct A{ bool have_value; B b;
void serialize(Ar &ar){ ar & have_value; if(have_value) ar & b; } };
that's valid serialization code and introduces a new table column at runtime if the object is mapped to a rdb and only objects with !have_value have been serialized so far.
True, fully static approaches will create the column even if it's never used.
how did you plan to represent views generated by a SELECT query? because the query results can contain columns from different tables so you'd have to have a "dynamic" row type anyway. (unless you tried to deduce the row type from the query type?)
Exactly. My `select' construct remembers all the types that were presented to it. Constructs like views and subselects will be statically checked. Errors like using in the `values' clause a column from another table in an insert statement, or a column from the same table but of the wrong type are also caught at compile-time. I guess that one could also make a compile-time assertion that validates an entire schema. J-L