I always included this in my longest consensus branches because it was free to do so when you where changing the function's footprint anyway, but I lost it in rebase because I though it was purely a question of style (using const before or after). It turns out it is not just about complying with our current style: the parameter could be const but is not.
Libconsensus related: ping @NicolasDorier @kanzure (feel free to ask to be added to this little list).
Concept ACK
ACK 6f3d616 (I thought there was a subtle difference between const CBlockIndex* pindexPrev and CBlockIndex* const pindexPrev that only C Jedi could understand, but it is fine)
@NicolasDorier: no, the first is a pointer to a const CBlockIndex. The second is a const pointer to a non-const CBlockIndex.
utACK
utACK 6f3d616
@NicolasDorier: no, the first is a pointer to a const CBlockIndex. The second is a const pointer to a non-const CBlockIndex.
Actually, I don't think the const after does anything at all. Note that the declaration of ContextualCheckBlock didn't had any const in it, but the definition had it. It seems to me that the const in the definition must be ignored or else it wouldn't link for not matching the declaration.
ACK 6f3d616
Extending on the meta discussion, if I understand it correctly, it works like this:
const Object* and const Object& are equivalent: you can neither change the state of the object nor change the address in memory the pointer is pointing to.
With Object& you can change the state of the object, but not the pointer.
With Object* you can both change the state of the object and change the memory address the pointers points to.
@jtimon (possibly misunderstanding your point) const Object* is only const on the object, not the pointer itself. The pointer itself can be modified.
that said, utACK https://github.com/bitcoin/bitcoin/commit/6f3d616dc8d6840c2293ffadd8cc3209f1100193
@instagibbs so in my little example, ptr will be &B after calling the function? https://0bin.net/paste/qfBVja+dQAt-R56h#BbZHm3Ynf3rkl01YLVU+tgPKggTbeVMvarzFk-LhFDN
@jtimon You have two variables named ptr there. A global one, and one inside testFunction. When testFunction is called, its argument (ptr) is evaluated (resulting in &A), and the value &A is passed to the function, which binds it to the parameter ptr. Executing ptr = &B modifies the local variable ptr, but not the global one (as the argument is passed by value, not by reference).
@sipa Right, which is what I was saying to @instagibbs , that the pointer would not be modified with const. But if you s/const Object* ptr/Object* ptr/ then the local ptr will be changed. Right? Is my comment #8347 (comment) incorrect ?
utACK 6f3d616