This PR marks all of the core data identity classes as const to reflect that these types are effectively immutable.
As noted elsewhere, compound_identity has a small degree of technical mutability due to lazy initialization, and virtual_identity has mutability due to its dual purpose for implementing vtable interposes; these are both accommodated by marking the related class members as mutable. This results in some const_casts, in the compound_identity and struct_identity constructors, and in a couple of places in code related to virtual identities. There are also several const_casts associated with storing type identity pointers into Lua metatables and lightuserdata objects, which are downcasts into void* and thus have to be const_casted to maintain correctness. Some of these are arguably code smells arguing for a redesign of the code in question, but that's for a future PR.
I also rewrote a couple of methods in VMethodInterposeLinkBase to avoid using map::operator[] (because the latter breaks constness); this has the side effect that searching for a vmethod by index will no longer insert an empty pointer into a virtual class's vtable interpose map on a lookup for a previously undefined index.
While these changes will enable making a significant fraction of data_identity instances constinit or constexpr (which has advantages in terms of more predictable static initialization, faster startup, and possibly other optimizations), such changes are not included in this PR.
This PR marks all of the core data identity classes as
constto reflect that these types are effectively immutable.As noted elsewhere,
compound_identityhas a small degree of technical mutability due to lazy initialization, andvirtual_identityhas mutability due to its dual purpose for implementing vtable interposes; these are both accommodated by marking the related class members asmutable. This results in someconst_casts, in thecompound_identityandstruct_identityconstructors, and in a couple of places in code related to virtual identities. There are also severalconst_casts associated with storing type identity pointers into Lua metatables and lightuserdata objects, which are downcasts intovoid*and thus have to beconst_casted to maintain correctness. Some of these are arguably code smells arguing for a redesign of the code in question, but that's for a future PR.I also rewrote a couple of methods in
VMethodInterposeLinkBaseto avoid usingmap::operator[](because the latter breaksconstness); this has the side effect that searching for a vmethod by index will no longer insert an empty pointer into a virtual class's vtable interpose map on a lookup for a previously undefined index.While these changes will enable making a significant fraction of
data_identityinstancesconstinitorconstexpr(which has advantages in terms of more predictable static initialization, faster startup, and possibly other optimizations), such changes are not included in this PR.