[ 2010-02-07 Original wording saved here: ]

Option 1:

The problem can be eliminated by omitting the requirement that a.erase(q) return an iterator. This is, however, in contrast with the equivalent requirements for other standard containers.

Option 2:

a.erase(q) can be made to compute the next iterator only when explicitly requested: the technique consists in returning a proxy object implicitly convertible to iterator, so that

iterator q1=a.erase(q);

works as expected, while

a.erase(q);

does not ever invoke the conversion-to-iterator operator, thus avoiding the associated computation. To allow this technique, some sections of TR1 along the line "return value is an iterator..." should be changed to "return value is an unspecified object implicitly convertible to an iterator..." Although this trick is expected to work transparently, it can have some collateral effects when the expression a.erase(q) is used inside generic code.