- preparations for null pointer support.

- add pointer support to FxAssign.

src/dobjtype.cpp

@@ -84,6 +84,7 @@ PColor *TypeColor;
 PStatePointer *TypeState;
 PStruct *TypeVector2;
 PStruct *TypeVector3;
+PPointer *TypeNullPtr;
 
 // PRIVATE DATA DEFINITIONS ------------------------------------------------
 
@@ -616,6 +617,7 @@ void PType::StaticInit()
 	TypeTable.AddType(TypeSound = new PSound);
 	TypeTable.AddType(TypeColor = new PColor);
 	TypeTable.AddType(TypeState = new PStatePointer);
+	TypeTable.AddType(TypeNullPtr = new PPointer);
 
 	TypeVector2 = new PStruct(NAME_Vector2, nullptr);
 	TypeVector2->AddField(NAME_X, TypeFloat64);
@@ -1635,7 +1637,7 @@ END_POINTERS
 PPointer::PPointer()
 : PBasicType(sizeof(void *), __alignof(void *)), PointedType(NULL)
 {
-	mDescriptiveName = "Pointer";
+	mDescriptiveName = "NullPointer";
 }
 
 //==========================================================================

src/dobjtype.h

@@ -530,6 +530,7 @@ class PPointer : public PBasicType
 	DECLARE_CLASS(PPointer, PBasicType);
 	HAS_OBJECT_POINTERS;
 public:
+	PPointer();
 	PPointer(PType *pointsat);
 
 	PType *PointedType;
@@ -546,7 +547,6 @@ public:
 	bool ReadValue(FSerializer &ar, const char *key,void *addr) const override;
 
 protected:
-	PPointer();
 };
 
 class PClassPointer : public PPointer
@@ -890,6 +890,7 @@ extern PColor *TypeColor;
 extern PStruct *TypeVector2;
 extern PStruct *TypeVector3;
 extern PStatePointer *TypeState;
+extern PPointer *TypeNullPtr;
 
 // A constant value ---------------------------------------------------------
 

src/scripting/codegeneration/codegen.cpp

@@ -1078,6 +1078,10 @@ FxExpression *FxTypeCast::Resolve(FCompileContext &ctx)
 		// don't go through the entire list if the types are the same.
 		goto basereturn;
 	}
+	else if (basex->ValueType == TypeNullPtr && (ValueType == TypeState || ValueType->IsKindOf(RUNTIME_CLASS(PPointer))))
+	{
+		goto basereturn;
+	}
 	else if (ValueType->GetRegType() == REGT_FLOAT)
 	{
 		FxExpression *x = new FxFloatCast(basex);
@@ -1199,6 +1203,7 @@ basereturn:
 	auto x = basex;
 	basex = nullptr;
 	delete this;
+	x->ValueType = ValueType;
 	return x;
 
 }
@@ -1772,19 +1777,8 @@ FxExpression *FxAssign::Resolve(FCompileContext &ctx)
 
 	SAFE_RESOLVE(Right, ctx);
 
-	if (!Base->IsNumeric() || !Right->IsNumeric())
+	if (Base->IsNumeric() && Right->IsNumeric())
 	{
-		ScriptPosition.Message(MSG_ERROR, "Numeric type expected");
-		delete this;
-		return nullptr;
-	}
-	if (!Base->RequestAddress(&AddressWritable) || !AddressWritable)
-	{
-		ScriptPosition.Message(MSG_ERROR, "Expression must be a modifiable value");
-		delete this;
-		return nullptr;
-	}
-
 		if (Right->ValueType != ValueType)
 		{
 			if (ValueType == TypeBool)
@@ -1801,6 +1795,56 @@ FxExpression *FxAssign::Resolve(FCompileContext &ctx)
 			}
 			SAFE_RESOLVE(Right, ctx);
 		}
+	}
+	else if (Base->ValueType == Right->ValueType)
+	{
+		if (Base->ValueType->IsKindOf(RUNTIME_CLASS(PArray)))
+		{
+			ScriptPosition.Message(MSG_ERROR, "Cannot assign arrays");
+			delete this;
+			return nullptr;
+		}
+		if (Base->ValueType->IsKindOf(RUNTIME_CLASS(PStruct)))
+		{
+			ScriptPosition.Message(MSG_ERROR, "Struct assignment not implemented yet");
+			delete this;
+			return nullptr;
+		}
+		// Both types are the same so this is ok.
+	}
+	else if ((Base->ValueType == TypeState || Base->ValueType->IsKindOf(RUNTIME_CLASS(PPointer))) && Right->ValueType == TypeNullPtr)
+	{
+		// null pointers can be assigned to any other pointer
+	}
+	else if (Base->ValueType->IsKindOf(RUNTIME_CLASS(PClassPointer)))
+	{
+		// class pointers may be assignable so add a cast which performs a check.
+		Right = new FxClassTypeCast(static_cast<PClassPointer *>(ValueType), Right);
+		SAFE_RESOLVE(Right, ctx);
+	}
+	else if (Base->ValueType == TypeString && (Right->ValueType == TypeName || Right->ValueType == TypeSound))
+	{
+		Right = new FxStringCast(Right);
+		SAFE_RESOLVE(Right, ctx);
+	}
+	else if (Base->ValueType == TypeName && Right->ValueType == TypeString)
+	{
+		Right = new FxNameCast(Right);
+		SAFE_RESOLVE(Right, ctx);
+	}
+	else
+	{
+		ScriptPosition.Message(MSG_ERROR, "Assignment between incompatible types.");
+		delete this;
+		return nullptr;
+	}
+	if (!Base->RequestAddress(&AddressWritable) || !AddressWritable)
+	{
+		ScriptPosition.Message(MSG_ERROR, "Expression must be a modifiable value");
+		delete this;
+		return nullptr;
+	}
+
 
 	return this;
 }
@@ -1808,7 +1852,7 @@ FxExpression *FxAssign::Resolve(FCompileContext &ctx)
 ExpEmit FxAssign::Emit(VMFunctionBuilder *build)
 {
 	static const BYTE loadops[] = { OP_LK, OP_LKF, OP_LKS, OP_LKP };
-	assert(ValueType == Base->ValueType && IsNumeric());
+	assert(ValueType == Base->ValueType);
 	assert(ValueType->GetRegType() == Right->ValueType->GetRegType());
 
 	ExpEmit pointer = Base->Emit(build);
@@ -2272,8 +2316,14 @@ FxExpression *FxPow::Resolve(FCompileContext& ctx)
 {
 	CHECKRESOLVED();
 
-	if (!ResolveLR(ctx, true)) return NULL;
+	if (!ResolveLR(ctx, true)) return nullptr;
 
+	if (!IsNumeric())
+	{
+		ScriptPosition.Message(MSG_ERROR, "Numeric type expected");
+		delete this;
+		return nullptr;
+	}
 	if (left->isConstant() && right->isConstant())
 	{
 		double v1 = static_cast<FxConstant *>(left)->GetValue().GetFloat();
@@ -6015,6 +6065,14 @@ FxExpression *FxClassTypeCast::Resolve(FCompileContext &ctx)
 	CHECKRESOLVED();
 	SAFE_RESOLVE(basex, ctx);
 
+	if (basex->ValueType == TypeNullPtr)
+	{
+		basex->ValueType = ValueType;
+		auto x = basex;
+		basex = nullptr;
+		delete this;
+		return x;
+	}
 	if (basex->ValueType->GetClass() == RUNTIME_CLASS(PClassPointer))
 	{
 		auto to = static_cast<PClassPointer *>(ValueType);

src/scripting/codegeneration/codegen.h

@@ -380,6 +380,13 @@ public:
 		isresolved = true;
 	}
 
+	FxConstant(nullptr_t *nullp, const FScriptPosition &pos) : FxExpression(pos)
+	{
+		value.pointer = nullptr;
+		ValueType = value.Type = TypeNullPtr;
+		isresolved = true;
+	}
+	
 	static FxExpression *MakeConstant(PSymbol *sym, const FScriptPosition &pos);
 
 	bool isConstant() const