From 929e4e630a5e2151425bc89b67adec48b0a15909 Mon Sep 17 00:00:00 2001
From: Jacek Sieka <arnetheduck@gmail.com>
Date: Sat, 18 Jan 2025 17:42:00 +1300
Subject: [PATCH] Simplify delete

The subclassing structure in `miqt` is such that nothing ever inherits
from `MiqtVirtual` - also, for `MiqtVirtual` to work correctly when Qt
deletes an instance part of a tree of widgets, the technique can only be
used with types that already have a virtual destructor.

Therefore:
* make `MiqtVirtual` final to ensure nothing inherits from it by
accident
* remove `virtual` inheritance of its base class - since there is no MI
invonved and no further inheritance, there can also not be any diamond
inheritance structures - removing `virtual` makes inheritance a bit
cheaper
* remove `isSubclass` from `delete` function - C++ already calls the
most inherited destructor
* mark destructor `override` to verify said assumption
---
 cmd/genbindings/emitcabi.go | 16 +++++++---------
 cmd/genbindings/emitgo.go   |  2 +-
 2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/cmd/genbindings/emitcabi.go b/cmd/genbindings/emitcabi.go
index c1c16064..32f84bae 100644
--- a/cmd/genbindings/emitcabi.go
+++ b/cmd/genbindings/emitcabi.go
@@ -756,7 +756,7 @@ extern "C" {
 
 		// delete
 		if c.CanDelete {
-			ret.WriteString(fmt.Sprintf("void %s_Delete(%s* self, bool isSubclass);\n", methodPrefixName, methodPrefixName))
+			ret.WriteString(fmt.Sprintf("void %s_Delete(%s* self);\n", methodPrefixName, methodPrefixName))
 		}
 
 		ret.WriteString("\n")
@@ -865,7 +865,7 @@ extern "C" {
 
 			overriddenClassName := "MiqtVirtual" + strings.Replace(cppClassName, `::`, ``, -1)
 
-			ret.WriteString("class " + overriddenClassName + " : public virtual " + cppClassName + " {\n" +
+			ret.WriteString("class " + overriddenClassName + " final : public " + cppClassName + " {\n" +
 				"public:\n" +
 				"\n",
 			)
@@ -885,7 +885,7 @@ extern "C" {
 				)
 			} else {
 				ret.WriteString(
-					"\tvirtual ~" + overriddenClassName + "() = default;\n" +
+					"\tvirtual ~" + overriddenClassName + "() override = default;\n" +
 						"\n",
 				)
 			}
@@ -1217,14 +1217,12 @@ extern "C" {
 		}
 
 		// Delete
+		// If we subclassed, our class destructor is always virtual. Therefore
+		// we can delete from the self ptr without any dynamic_cast<>
 		if c.CanDelete {
 			ret.WriteString(
-				"void " + methodPrefixName + "_Delete(" + methodPrefixName + "* self, bool isSubclass) {\n" +
-					"\tif (isSubclass) {\n" +
-					"\t\tdelete dynamic_cast<" + cppClassName + "*>( self );\n" +
-					"\t} else {\n" +
-					"\t\tdelete self;\n" +
-					"\t}\n" +
+				"void " + methodPrefixName + "_Delete(" + methodPrefixName + "* self) {\n" +
+					"\tdelete self;\n" +
 					"}\n" +
 					"\n",
 			)
diff --git a/cmd/genbindings/emitgo.go b/cmd/genbindings/emitgo.go
index d90316da..cb5a6774 100644
--- a/cmd/genbindings/emitgo.go
+++ b/cmd/genbindings/emitgo.go
@@ -1074,7 +1074,7 @@ import "C"
 			ret.WriteString(`
 			// Delete this object from C++ memory.
 			func (this *` + goClassName + `) Delete() {
-				C.` + goClassName + `_Delete(this.h, C.bool(this.isSubclass))
+				C.` + goClassName + `_Delete(this.h)
 			}
 				
 			// GoGC adds a Go Finalizer to this pointer, so that it will be deleted