My advice on implementing stuff in C: [LWN.net]

My advice on implementing stuff in C:

Posted Oct 15, 2010 19:20 UTC (Fri) by mjthayer (guest, #39183)
In reply to: My advice on implementing stuff in C: by HelloWorld
Parent article: Russell: On C Library Implementation

> Also, I don't see your point about virtual inheritance. It was added to the language in order to solve the diamond inheritance problem, which occurs very rarely anyway, and it does solve that problem for me.

I'm wondering if I understood dskoll correctly, but pure virtual classes are actually one of the things in C++ that I find good without having to qualify. I find that inheriting behaviour often makes code harder to understand without a good reason.

I do like the way go handles this with its semi-implicit interfaces (from reading about it, not actually programming in it). But of course go is still too young and little used for people to have discovered its warts.

to post comments

My advice on implementing stuff in C:

Posted Oct 18, 2010 0:10 UTC (Mon) by HelloWorld (guest, #56129) [Link]

I'm wondering if I understood dskoll correctly,

I don't think so. I think that dskoll was talking about virtual inheritance. Say, you have code such as this:

struct A { int a; };
struct D1 : A { int d1; };
struct D2 : A { int d2; };
struct B : D1, D2 { int b; };

Then, B will inherit A::a twice, once from D1 and once from D2. So, inside B, you'll actually have two fields named a, and if you want to use one of them, you always have to use full qualification, that is, you have to write D1::a or D2::a instead of just plain a. Virtual inheritance solves this problem. If you change the code as follows,

struct A { int a; };
struct D1 : virtual A { int d1; };
struct D2 : virtual A { int d2; };
struct B : D1, D2 { int b; };

then the two A sub-objects in B will be collapsed to a single one. It's also explained in the C++ FAQ lite: http://www.parashift.com/c++-faq-lite/multiple-inheritance.html