Hi all,
C++ multiple inheritance is not discussed in the documentation and there are
only very old issues in the emscripten issue tracker. From what I read so far
is that multiple inheritance is not supported in embind because JS does not
support that. That's not false, but MI is used so often in C++ there must be a
workaround (and I'm looking for one).
In my case I have `class Lexer : public Recognizer, public TokenSource {}`. In
some places I need that lexer as a recognizer and in some I need it as token
source. My bindings are like this (simplified):
class_<Lexer, base<Recognizer>>("Lexer$Internal")
.property("mode", &Lexer::mode);
class_<LexerHelper, base<Lexer>>("Lexer")
.constructor<CharStream *>()
.allow_subclass<LexerWrapper>("LexerWrapper", constructor<CharStream *>());
Since I cannot specify both classes as base in the bindings call, I started
with `base<Recognizer>` which works fine. However, when I try to use the lexer
class in a place where a token source is required, I get the error:
BindingError: Expected null or instance of TokenSource, got an instance of
Recognizer
at throwBindingError (file:... <>)
Side note: that approach to use `Lexer$Internal` and `LexerHelper` comes from
the fact that `Lexer` is an abstract class, but I need to bind its constructor
to allow calling that from JS where I use the Lexer to derive a JS class from.
So, I created the (non-abstract) `LexerHelper` class and pretend it's the
actual lexer class.
IIUC the error is bogus, because the checked class indeed derives from both
base classes, only JS doesn't know that. What can I do to make this scenario
work?
I experimented with leaving out the `Lexer` binding entirely (to avoid the MI
dilemma), but that only caused the generated JS class to be not extendable.
Mike
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