On 26/01/20 10:11, Marc-André Lureau wrote: >> I’m still puzzled as to why anybody would switch to something like >> GObject when there is C++. > C++ is another level of complexity. > > Replacing QOM with GObject would mainly bring us a more solid type > system with better tooling/features, gobject-introspection support, > and remove the burden of having our own OO from QEMU code base.
In fact, C++ doesn't solve any of the problems that either QOM or GObject try to solve. (Neither does Rust for that matter). Nevertheless, there is no stupid question, only stupid answers, and I think Christophe's remark is an example of a common misconception. In the hope of not making this a stupid answer, let my try to formulate succinctly what I think the differences are between QOM, GObject and the C++ object model: - the C++ object model (at least "old-style" C++ with virtual functions and the like) provides you with _the intersection_ of what QOM and GObject try to solve. This is what Marc-André calls "OO", and it's essentially virtual functions and dynamic casts. It's a relatively small part of both QOM and GObject, and unfortunately a wheel that almost every large C program ends up reinventing. - Marc-André also described above what GObject provides: a fully introspectable type system and the tools so that _libraries_ can define _types that will be used from multiple programming languages_. - QOM also provides a fully introspectable type system, but with a different focus: it's so that _objects_ can expose _properties that will be accessed from multiple channels_. Everything else in both GObject and QOM follows from this core purpose, and the differences between the two follow from the differences. For example: - GObject's focus on multiple programming languages: gobject-introspection, GClosure, support for non-object types (scalar and GBoxed) - QOM's focus on objects: dynamic properties, object tree, all types are classes - QOM's focus on properties: no introspection of methods - QOM's support for multiple channels: visitors Paolo
