Introduce immutable objects

Allow to 'freeze' objects which will raise a runtime error on
trying to modify them.

Immutability flags is applied to SQObject, which is a handle
referencing an actual container, just like const reference in C++.
So the object possibly can be mutated by the external code (again
like in C++)

The immutability is propagated to nested fields during get operation,
so if table t={w={x=123}} is immutable, t.w is also immutable.

A new _flags field was added added to SQObject.
When SQInteger is 64-bit (which in case of Dagor engine is true
both on 32 and 64 bit platform) it doesn't affect size of SQObject
struct.
On 32 bit platform with 32-bit SQInteger it currently increases
struct size from 8 to 12 bytes. If needed _flags may be packed
together with _type field (since together they need 28+1 bits),
or alternatively NaN tagging may be used.

Squirrel API added:

  freeze(object) - make a immutable object handle
  getobjflags(object) - return object flags

Also SQOBJ_FLAG_IMMUTABLE was added to const table

Author: VasiliyRyabtsev

include/sqconfig.h

@@ -1,4 +1,11 @@
 
+#if !defined(_MSC_VER) || defined(__clang__) || (_MSC_VER >= 1800)
+#define USE_STDINT
+#endif
+
+#ifdef USE_STDINT
+#include <stdint.h>
+#endif
 #ifdef _SQ64
 
 #ifdef _MSC_VER

include/squirrel.h

@@ -82,6 +82,8 @@ struct SQOuter;
 #define SQOBJECT_DELEGABLE      0x02000000
 #define SQOBJECT_CANBEFALSE     0x01000000
 
+#define SQOBJ_FLAG_IMMUTABLE    0x01
+
 #define SQ_MATCHTYPEMASKSTRING (-99999)
 
 #define _RT_MASK 0x00FFFFFF
@@ -127,6 +129,8 @@ typedef enum tagSQObjectType{
     OT_OUTER =          (_RT_OUTER|SQOBJECT_REF_COUNTED) //internal usage only
 }SQObjectType;
 
+typedef uint8_t SQObjectFlags;
+
 #define ISREFCOUNTED(t) ((t)&SQOBJECT_REF_COUNTED)
 
 
@@ -157,6 +161,7 @@ typedef union tagSQObjectValue
 typedef struct tagSQObject
 {
     SQObjectType _type;
+    SQObjectFlags _flags;
     SQObjectValue _unVal;
 }SQObject;
 
@@ -325,6 +330,7 @@ SQUIRREL_API SQRESULT sq_setfreevariable(HSQUIRRELVM v,SQInteger idx,SQUnsignedI
 SQUIRREL_API SQRESULT sq_next(HSQUIRRELVM v,SQInteger idx);
 SQUIRREL_API SQRESULT sq_getweakrefval(HSQUIRRELVM v,SQInteger idx);
 SQUIRREL_API SQRESULT sq_clear(HSQUIRRELVM v,SQInteger idx);
+SQUIRREL_API SQRESULT sq_freeze(HSQUIRRELVM v, SQInteger idx);
 
 /*calls*/
 SQUIRREL_API SQRESULT sq_call(HSQUIRRELVM v,SQInteger params,SQBool retval,SQBool invoke_err_handler);
@@ -397,6 +403,7 @@ SQUIRREL_API void sq_setnativedebughook(HSQUIRRELVM v,SQDEBUGHOOK hook);
 #define sq_isbool(o) ((o)._type==OT_BOOL)
 #define sq_isweakref(o) ((o)._type==OT_WEAKREF)
 #define sq_type(o) ((o)._type)
+#define sq_objflags(o) ((o)._flags)
 
 
 #define SQ_OK (0)

squirrel/sqapi.cpp

@@ -142,7 +142,7 @@ SQRESULT sq_compile(HSQUIRRELVM v,SQLEXREADFUNC read,SQUserPointer p,const SQCha
 #ifndef NO_COMPILER
     if(Compile(v, read, p, bindings, sourcename, o, raiseerror?true:false, _ss(v)->_debuginfo)) {
         v->Push(SQClosure::Create(_ss(v), _funcproto(o),
-                _table(v->_roottable)->GetWeakRef(_ss(v)->_alloc_ctx, OT_TABLE)));
+                _table(v->_roottable)->GetWeakRef(_ss(v)->_alloc_ctx, OT_TABLE, 0)));
         return SQ_OK;
     }
     return SQ_ERROR;
@@ -482,7 +482,7 @@ SQRESULT sq_bindenv(HSQUIRRELVM v,SQInteger idx)
         !sq_isclass(env) &&
         !sq_isinstance(env))
         return sq_throwerror(v,_SC("invalid environment"));
-    SQWeakRef *w = _refcounted(env)->GetWeakRef(_ss(v)->_alloc_ctx, sq_type(env));
+    SQWeakRef *w = _refcounted(env)->GetWeakRef(_ss(v)->_alloc_ctx, sq_type(env), env._flags);
     SQObjectPtr ret;
     if(sq_isclosure(o)) {
         SQClosure *c = _closure(o)->Clone();
@@ -529,7 +529,7 @@ SQRESULT sq_setclosureroot(HSQUIRRELVM v,SQInteger idx)
     SQObject o = stack_get(v, -1);
     if(!sq_isclosure(c)) return sq_throwerror(v, _SC("closure expected"));
     if(sq_istable(o)) {
-        _closure(c)->SetRoot(_table(o)->GetWeakRef(_ss(v)->_alloc_ctx, OT_TABLE));
+        _closure(c)->SetRoot(_table(o)->GetWeakRef(_ss(v)->_alloc_ctx, OT_TABLE, o._flags));
         v->Pop();
         return SQ_OK;
     }
@@ -934,6 +934,12 @@ SQRESULT sq_rawset(HSQUIRRELVM v,SQInteger idx)
         v->Pop(2);
         return sq_throwerror(v, _SC("null key"));
     }
+
+    if (self._flags & SQOBJ_FLAG_IMMUTABLE) {
+        v->Raise_Error(_SC("trying to modify immutable '%s'"),GetTypeName(self));
+        return SQ_ERROR;
+    }
+
     switch(sq_type(self)) {
     case OT_TABLE:
         _table(self)->NewSlot(key, v->GetUp(-1));
@@ -1028,6 +1034,12 @@ SQRESULT sq_rawdeleteslot(HSQUIRRELVM v,SQInteger idx,SQBool pushval)
     sq_aux_paramscheck(v, 2);
     SQObjectPtr *self;
     _GETSAFE_OBJ(v, idx, OT_TABLE,self);
+
+    if (self->_flags & SQOBJ_FLAG_IMMUTABLE) {
+        v->Raise_Error(_SC("trying to modify immutable '%s'"),GetTypeName(*self));
+        return SQ_ERROR;
+    }
+
     SQObjectPtr &key = v->GetUp(-1);
     SQObjectPtr t;
     if(_table(*self)->Get(key,t)) {
@@ -1168,7 +1180,7 @@ void sq_pushobject(HSQUIRRELVM v,HSQOBJECT obj)
 
 void sq_resetobject(HSQOBJECT *po)
 {
-    po->_unVal.raw=0;po->_type=OT_NULL;
+    po->_unVal.raw=0;po->_type=OT_NULL;po->_flags=0;
 }
 
 SQRESULT sq_throwerror(HSQUIRRELVM v,const SQChar *err)
@@ -1532,7 +1544,7 @@ void sq_weakref(HSQUIRRELVM v,SQInteger idx)
 {
     SQObject &o=stack_get(v,idx);
     if(ISREFCOUNTED(sq_type(o))) {
-        v->Push(_refcounted(o)->GetWeakRef(_ss(v)->_alloc_ctx, sq_type(o)));
+        v->Push(_refcounted(o)->GetWeakRef(_ss(v)->_alloc_ctx, sq_type(o), o._flags));
         return;
     }
     v->Push(o);
@@ -1611,6 +1623,21 @@ void sq_move(HSQUIRRELVM dest,HSQUIRRELVM src,SQInteger idx)
     dest->Push(stack_get(src,idx));
 }
 
+SQRESULT sq_freeze(HSQUIRRELVM v, SQInteger idx)
+{
+    SQObjectPtr &o = stack_get(v, idx);
+    SQObjectType tp = sq_type(o);
+    if (tp != OT_ARRAY && tp != OT_TABLE && tp != OT_INSTANCE && tp != OT_CLASS && tp != OT_USERDATA) {
+        v->Raise_Error(_SC("Cannot freeze %s"), IdType2Name(tp));
+        return SQ_ERROR;
+    }
+
+    SQObjectPtr dst = o;
+    dst._flags |= SQOBJ_FLAG_IMMUTABLE;
+    v->Push(dst);
+    return SQ_OK;
+}
+
 void sq_setprintfunc(HSQUIRRELVM v, SQPRINTFUNCTION printfunc,SQPRINTFUNCTION errfunc)
 {
     _ss(v)->_printfunc = printfunc;

squirrel/sqbaselib.cpp

@@ -22,6 +22,15 @@ static SQInteger delegable_getfuncinfos(HSQUIRRELVM v);
 static SQInteger class_getfuncinfos(HSQUIRRELVM v);
 
 
+#define SQ_CHECK_IMMUTABLE_SELF \
+    if (sq_objflags(stack_get(v,1)) & SQOBJ_FLAG_IMMUTABLE) \
+        return sq_throwerror(v, _SC("Cannot modify immutable object"));
+
+#define SQ_CHECK_IMMUTABLE_OBJ(o) \
+    if (sq_objflags(o) & SQOBJ_FLAG_IMMUTABLE) \
+        return sq_throwerror(v, _SC("Cannot modify immutable object"));
+
+
 static bool str2num(const SQChar *s,SQObjectPtr &res,SQInteger base)
 {
     SQChar *end;
@@ -373,6 +382,17 @@ static SQInteger base_clamp(HSQUIRRELVM v)
     return 1;
 }
 
+static SQInteger base_freeze(HSQUIRRELVM v)
+{
+    return SQ_SUCCEEDED(sq_freeze(v, 2)) ? 1 : SQ_ERROR;
+}
+
+static SQInteger base_getobjflags(HSQUIRRELVM v)
+{
+    sq_pushinteger(v, sq_objflags(stack_get(v, 2)));
+    return 1;
+}
+
 
 static const SQRegFunction base_funcs[]={
     //generic
@@ -400,6 +420,8 @@ static const SQRegFunction base_funcs[]={
     {_SC("min"),base_min_max<-1>,-3,_SC(".nnnnnnnn")},
     {_SC("max"),base_min_max<1>,-3,_SC(".nnnnnnnn")},
     {_SC("clamp"),base_clamp,4,_SC(".nnn")},
+    {_SC("freeze"),base_freeze,2,NULL},
+    {_SC("getobjflags"), base_getobjflags,2,NULL},
     {NULL,(SQFUNCTION)0,0,NULL}
 };
 
@@ -509,6 +531,7 @@ static SQInteger obj_delegate_weakref(HSQUIRRELVM v)
 
 static SQInteger obj_clear(HSQUIRRELVM v)
 {
+    SQ_CHECK_IMMUTABLE_SELF;
     return SQ_SUCCEEDED(sq_clear(v,-1)) ? 1 : SQ_ERROR;
 }
 
@@ -524,6 +547,8 @@ static SQInteger number_delegate_tochar(HSQUIRRELVM v)
 
 static SQInteger container_update(HSQUIRRELVM v)
 {
+    SQ_CHECK_IMMUTABLE_SELF;
+
     SQInteger top = sq_gettop(v);
     for (int arg=2; arg<=top; ++arg) {
         SQObjectType argType = sq_gettype(v, arg);
@@ -545,9 +570,10 @@ static SQInteger container_update(HSQUIRRELVM v)
 
 static SQInteger container_merge(HSQUIRRELVM v)
 {
+    SQObject &o = stack_get(v,1);
+
     SQInteger top = sq_gettop(v);
-    SQObjectType tp = sq_gettype(v, 1);
-    switch (tp) {
+    switch (sq_type(o)) {
         case OT_TABLE:
             sq_newtableex(v, sq_getsize(v, 1));
             break;
@@ -673,6 +699,8 @@ static SQInteger container_findvalue(HSQUIRRELVM v)
 
 static SQInteger table_rawdelete(HSQUIRRELVM v)
 {
+    SQ_CHECK_IMMUTABLE_SELF;
+
     if(SQ_FAILED(sq_rawdeleteslot(v,1,SQTrue)))
         return SQ_ERROR;
     return 1;
@@ -691,6 +719,8 @@ static SQInteger container_rawexists(HSQUIRRELVM v)
 
 static SQInteger container_rawset(HSQUIRRELVM v)
 {
+    SQ_CHECK_IMMUTABLE_SELF;
+
     return SQ_SUCCEEDED(sq_rawset(v,-3)) ? 1 : SQ_ERROR;
 }
 
@@ -700,6 +730,7 @@ static SQInteger container_rawget(HSQUIRRELVM v)
     return SQ_SUCCEEDED(sq_rawget(v,-2))?1:SQ_ERROR;
 }
 
+
 static SQInteger table_setdelegate(HSQUIRRELVM v)
 {
     if(SQ_FAILED(sq_setdelegate(v,-2)))
@@ -942,6 +973,8 @@ const SQRegFunction SQSharedState::_table_default_delegate_funcz[]={
 
 static SQInteger array_append(HSQUIRRELVM v)
 {
+    SQ_CHECK_IMMUTABLE_SELF;
+
     SQArray *arr = _array(stack_get(v, 1));
     SQInteger nitems = sq_gettop(v)-1;
     SQInteger offs = arr->Size();
@@ -955,6 +988,8 @@ static SQInteger array_append(HSQUIRRELVM v)
 
 static SQInteger array_extend(HSQUIRRELVM v)
 {
+    SQ_CHECK_IMMUTABLE_SELF;
+
     SQArray *arr = _array(stack_get(v, 1));
     SQInteger n = sq_gettop(v)-1;
     for (SQInteger i=0; i<n; ++i) {
@@ -969,11 +1004,15 @@ static SQInteger array_extend(HSQUIRRELVM v)
 
 static SQInteger array_reverse(HSQUIRRELVM v)
 {
+    SQ_CHECK_IMMUTABLE_SELF;
+
     return SQ_SUCCEEDED(sq_arrayreverse(v,-1)) ? 1 : SQ_ERROR;
 }
 
 static SQInteger array_pop(HSQUIRRELVM v)
 {
+    SQ_CHECK_IMMUTABLE_SELF;
+
     return SQ_SUCCEEDED(sq_arraypop(v,1,SQTrue))?1:SQ_ERROR;
 }
 
@@ -990,6 +1029,9 @@ static SQInteger array_top(HSQUIRRELVM v)
 static SQInteger array_insert(HSQUIRRELVM v)
 {
     SQObject &o=stack_get(v,1);
+
+    SQ_CHECK_IMMUTABLE_OBJ(o);
+
     SQObject &idx=stack_get(v,2);
     SQObject &val=stack_get(v,3);
     if(!_array(o)->Insert(tointeger(idx),val))
@@ -1001,6 +1043,8 @@ static SQInteger array_insert(HSQUIRRELVM v)
 static SQInteger array_remove(HSQUIRRELVM v)
 {
     SQObject &o = stack_get(v, 1);
+    SQ_CHECK_IMMUTABLE_OBJ(o);
+
     SQObject &idx = stack_get(v, 2);
     if(!sq_isnumeric(idx)) return sq_throwerror(v, _SC("wrong type"));
     SQObjectPtr val;
@@ -1015,6 +1059,8 @@ static SQInteger array_remove(HSQUIRRELVM v)
 static SQInteger array_resize(HSQUIRRELVM v)
 {
     SQObject &o = stack_get(v, 1);
+    SQ_CHECK_IMMUTABLE_OBJ(o);
+
     SQObject &nsize = stack_get(v, 2);
     SQObjectPtr fill;
     if(sq_isnumeric(nsize)) {
@@ -1079,6 +1125,8 @@ static SQInteger array_map(HSQUIRRELVM v)
 static SQInteger array_apply(HSQUIRRELVM v)
 {
     SQObject &o = stack_get(v,1);
+    SQ_CHECK_IMMUTABLE_OBJ(o);
+
     if(SQ_FAILED(__map_array(_array(o),_array(o),v,false)))
         return SQ_ERROR;
     sq_pop(v,1);
@@ -1299,6 +1347,8 @@ static SQInteger array_sort(HSQUIRRELVM v)
 {
     SQInteger func = -1;
     SQObjectPtr &o = stack_get(v,1);
+    SQ_CHECK_IMMUTABLE_OBJ(o);
+
     if(_array(o)->Size() > 1) {
         if(sq_gettop(v) == 2) func = 2;
         if(!_hsort(v, o, 0, _array(o)->Size()-1, func))
@@ -1346,6 +1396,8 @@ static SQInteger array_slice(HSQUIRRELVM v)
 
 static SQInteger array_replace(HSQUIRRELVM v)
 {
+    SQ_CHECK_IMMUTABLE_SELF;
+
     SQArray *dst = _array(stack_get(v, 1));
     SQArray *src = _array(stack_get(v, 2));
     dst->_values.copy(src->_values);
@@ -1380,7 +1432,6 @@ const SQRegFunction SQSharedState::_array_default_delegate_funcz[]={
     {_SC("findvalue"),container_findvalue,-2, _SC("ac.")},
     {_SC("totable"),pairs_to_table,1, _SC("a") },
     {_SC("replace"),array_replace,2, _SC("aa")},
-
     {NULL,(SQFUNCTION)0,0,NULL}
 };