1. Virtual base, constructor & destructor
Kei Hasegawa

2. Example V A B C struct C : A, B { }; struct V { ... C(int c) : A(c) {}
V(int);
~V(); };
struct A : virtual V {
A(int a) : V(a) { ... }
struct B : virtual V {
~B(); V A B C

3. Constructor of C Call default constructor of V that is common part
Nothing to be done if there doesn’t exist constructor of V
It’s error if V has non-default construct and doesn’t have default constructor
Call special version constructor of A and B which are base class of C:
not call constructor of V

4. Constructor of A struct A : virtual V { }; ... A(int a) : V(a) { ... }
Special version constructor
Called from constructor of C
Generated by compiler
Same with A(int) in spite of not calling constructor of V } };

5. Consturctor of B Basically same with A struct B : virtual V { }; ...
Generated by compiler
B has virtual base V or
V constructor is declared }
B’() {
Special version
Called from construct of C
Same with B() in spite of not calling constructor of V };

6. Destructor of C Call special version destructor of B and A
Not calling destructor of V
Call destructor of V which is common part
Nothing to be done if V has no destructor

7. Destructor of B struct B : virtual V { }; ... ~B(); ~B’() { }
Generated by compiler
Same with ~B() in spite of not calling ~V()
Called from constructor of C } };

8. Destructor of A Basically same with B struct A : virtual V { }; ...
Generated by compiler
~V() is declared }
~A’() {
Called from destructor of C
Same with ~A() in spite of not calling ~V()
If there exists nothing to be done, calling from destructor of C can be omitted. };

9. Implementation note
Number of special versions constructor & destructor is 2^n – 1, where n is number of virtual base
struct A : virtual V1, virtual V2, ..., virtual Vn {
... };
All these special versions shouldn’t be generated at compiling of A
When struct C is declared like example, special versions constructor & destructor of A and B are required. So, it’s reasonable to generate them when they are require.

10. Implementation abstract (1)
Enable to specify exclude list when generating base class constructor & destructor
struct V at example
Suppress inline substitution for exchanging special version constructor & destructor
C::C(int c) : A(c) { ... }
A(c) will be exchanged to special version

11. Implementation abstract (2)
Constructor & destructor of class which has virtual base
Generate inline function for body part
struct A : virtual V {
...
A(int a) : V(a) { /* Code here saved */ }
A.body(int a) { /* at this inline function */ } };
For special version of A::A(int)