If strings are immutable in L0x then this string representation: struct sObjString { Obj obj; int length; char* chars;

If strings are immutable in L0x then this string representation: struct sObjString { Obj obj; int length; char* chars; }; needlessly wastes 4 or 8 bytes for the chars pointer (among other heap management overhead related to separate allocations). Instead, I think, you should have struct sObjString { Obj obj; int length; char chars[0]; }; and allocate that string object as one chunk with its characters.