Obscure usages of C++ virtual inheritance -

the virtual inheritance in c++ useful way prevent diamond issue. however, can't seem make work in each , every case.

this going hard explain hope i'll manage. let's present problem:

a inherits b. , base class of class set called c , class set called d.

the problem c set of class have common features focusing around b.

what do, isn't possible, class e virtually inherits b, , inherited c. problem is:

in case, doesn't virtually inherits b. doesn't work.

if virtually inherit b, need use b's constructor in every classes of d.

conclusion: in every case there duplicated code. how may out of issue without duplicated code ?

okay saying have:

                             b                              +                              |                              v                                                           +                         +----+----+                         v         v                         c         d 

and of these non-virtual inheritance , have class e virtualy inherits b , c inherits complete diagram be:

                +-----------+b                 |            +                 |            |                 v            v                 e                            +            +                 +---+---+----+----+                     v             v                     c             d                                   

with exception b virtualy inherited e.

the solution simple should make a virtually inherit b, gathered question can not modify a. next option make c inherit a or e , have instance of other called delegation. alternative can provide common interface , allow polymorphism might want make interface (pure virtual class) has function in e c uses , make c , e derive interface. e implement virtual functions interface , c implement function calls e's implementation. alternatively (not recommended) can live diamond of death if not problematic you, determining tricky , don't recommend it's terrible idea.