Name Lookup Happens at Compile Time

The static type (§15.2.3, p. 601) of an object, reference, or pointer determines which members of that object are visible. Even when the static and dynamic types might differ (as can happen when a reference or pointer to a base class is used), the static type determines what members can be used. As an example, we might add a member to the Disc_quote class that returns a pair (§11.2.3, p. 426) holding the minimum (or maximum) quantity and the discounted price:

class Disc_quote : public Quote {
public:
    std::pair<size_t, double> discount_policy() const
        { return {quantity, discount}; }
    // other members as before
};

We can use discount_policy only through an object, pointer, or reference of type Disc_quote or of a class derived from Disc_quote:

Bulk_quote bulk;
Bulk_quote *bulkP = &bulk; //  static and dynamic types are the same
Quote *itemP = &bulk;      //  static and dynamic types differ
bulkP->discount_policy();  //  ok: bulkP has type Bulk_quote*
itemP->discount_policy();  //  error: itemP has type Quote*

Even though bulk has a member named discount_policy, that member is not visible through itemP. The type of itemP is a pointer to Quote, which means that the search for discount_policy starts in class Quote. The Quote class has no member named discount_policy, so we cannot call that member on an object, reference, or pointer of type Quote.