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5.4.7 Constant Declarations

The use of const in a declaration changes the sort of the object declared. In Larch/C++ the convention is to use the sort generator ConstObj instead of Obj. However, structs and unions are more complex, because const declarations for them mean that their top-level fields cannot be changed. Also the usual exception has to be made for arrays, because arrays are not themselves objects. For example, consider the following.

Declaration              Name    Its sort (when used as a global variable)
---------------------    ----    -----------------------------------------
const int ci = 7;        ci      ConstObj[int]
const int& rc = ci;      rc      ConstObj[int]
int i = 6;               i       Obj[int]
int& const cr = i;       cr      Obj[int]
const int * pci = &ci;   pci     Obj[Ptr[ConstObj[int]]]
int * const cip = &i;    cip     ConstObj[Ptr[Obj[int]]]
const int cai[3];        cpi     Arr[ConstObj[int]]
struct IPair {
  int fst, snd;
const IPair cp;          cp      ConstObj[Const[IPair]]
union IR {
  int i; float r;
const IR ir;             ir      ConstObj[Const[IR]]

The only reason for not making the sort of ci be int is that one can take the address of ci, whereas one cannot take the address of an integer value (such as 7). To get the abstract value, one has to use a state function; for example, the sort of ci^ and ci' is int.

The name rc is a reference to a constant integer object, and hence has the same sort as ci. The name cr is a constant reference to an integer object, but all references are unchanging in any case, so the use of const in its declaration is superfluous. This is why the sort of cr is the same as the sort of i.

The distinction between pointers to constants and constant pointers has more weight than the same distinction for references. Note that the sorts are different for pci (a pointer to a constant integer object) and cip (a constant pointer to an integer). The sort of *(pci') is ConstObj[int], while the sort of *(cip') is Obj[int].

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