virtual + inheritance example: remove multiple inheritance approach

It was already pretty badly intrusive, but it also appears to make MSVC
segfault.  Rather than investigating and fixing it, it's easier to just
remove it.

docs/advanced.rst

@@ -470,10 +470,6 @@ can now create a python class that inherits from ``Dog``:
     See the file :file:`example-virtual-functions.cpp` for complete examples
     using both the duplication and templated trampoline approaches.
 
-    The file also contains a more intrusive approach using multiple
-    inheritance, which may be useful in special situations with deep class
-    hierarchies to avoid code generation.
-
 .. _macro_notes:
 
 General notes regarding convenience macros

example/example-virtual-functions.cpp

@@ -82,20 +82,12 @@ void runExampleVirtVirtual(ExampleVirt *ex) {
 }
 
 
-// Inheriting virtual methods.  We do three versions here: the repeat-everything version and the
-// templated trampoline versions mentioned in docs/advanced.rst, and also another version using
-// multiple inheritance.
+// Inheriting virtual methods.  We do two versions here: the repeat-everything version and the
+// templated trampoline versions mentioned in docs/advanced.rst.
 //
-// This latter approach has the advantage of generating substantially less code for deep
-// hierarchies, but it requires intrusive changes of changing the wrapped classes to using virtual
-// inheritance, which itself requires constructor rewriting for any non-default virtual base class
-// constructors (most problematic is that constructors cannot be effectively inherited from a
-// virtual base class).  The example is kept here because it does work, and may be useful in limited
-// cases, but the non-instrusive templated version is generally preferred.
-//
-// These base classes are all exactly the same (aside from the virtual inheritance for the MI
-// version), but we technically need distinct classes for this example code because we need to be
-// able to bind them properly (pybind11, sensibly, doesn't allow us to bind the same C++ class to
+// These base classes are exactly the same, but we technically need distinct
+// classes for this example code because we need to be able to bind them
+// properly (pybind11, sensibly, doesn't allow us to bind the same C++ class to
 // multiple python classes).
 class A_Repeat {
 #define A_METHODS \
@@ -129,13 +121,6 @@ class D_Repeat : public C_Repeat {
 D_METHODS
 };
 
-// Base classes for multiple inheritance trampolines; note the added "virtual" inheritance.  The
-// classes are otherwise identical.
-class A_MI { A_METHODS };
-class B_MI : virtual public A_MI { B_METHODS };
-class C_MI : virtual public B_MI { C_METHODS };
-class D_MI : virtual public C_MI { D_METHODS };
-
 // Base classes for templated inheritance trampolines.  Identical to the repeat-everything version:
 class A_Tpl { A_METHODS };
 class B_Tpl : public A_Tpl { B_METHODS };
@@ -213,31 +198,6 @@ public:
 };
 */
 
-// Inheritance approach 3: multiple inheritance with virtual base class inheritance.  This requires
-// declaration and compilation of exactly 7 methods (one per virtual method declaration or
-// override), versus the 11 required above.  On the other hand, if we need anything other than
-// default constructors, this quickly becomes painful, and so this is of limited use.
-class PyA_MI : virtual public A_MI {
-public:
-    // Can't inherit constructors: we would have to duplicate constructors with an explicit
-    // initializer for each virtual base, which is a pain for anything but the default constructor.
-    int unlucky_number() override { PYBIND11_OVERLOAD_PURE(int, A_MI, unlucky_number, ); }
-    void say_something(unsigned times) override { PYBIND11_OVERLOAD(void, A_MI, say_something, times); }
-};
-class PyB_MI : public PyA_MI, virtual public B_MI {
-public:
-    void say_something(unsigned times) override { PYBIND11_OVERLOAD(void, B_MI, say_something, times); }
-    double lucky_number() { PYBIND11_OVERLOAD(double, B_MI, lucky_number, ); }
-    int unlucky_number() { PYBIND11_OVERLOAD(int, B_MI, unlucky_number, ); }
-};
-class PyC_MI : public PyB_MI, virtual public C_MI {
-public:
-    int unlucky_number() override { PYBIND11_OVERLOAD(int, C_MI, unlucky_number, ); }
-    double lucky_number() override { PYBIND11_OVERLOAD(double, C_MI, lucky_number, ); }
-};
-class PyD_MI : public PyC_MI, virtual public D_MI {
-};
-
 
 void initialize_inherited_virtuals(py::module &m) {
     // Method 1: repeat
@@ -266,19 +226,6 @@ void initialize_inherited_virtuals(py::module &m) {
     py::class_<D_Tpl, std::unique_ptr<D_Tpl>, PyB_Tpl<D_Tpl>>(m, "D_Tpl", py::base<C_Tpl>())
         .def(py::init<>());
 
-    // Method 3: MI
-    py::class_<A_MI, std::unique_ptr<A_MI>, PyA_MI>(m, "A_MI")
-        .def(py::init<>())
-        .def("unlucky_number", &A_MI::unlucky_number)
-        .def("say_something", &A_MI::say_something);
-    py::class_<B_MI, std::unique_ptr<B_MI>, PyB_MI>(m, "B_MI", py::base<A_MI>())
-        .def(py::init<>())
-        .def("lucky_number", &B_MI::lucky_number);
-    py::class_<C_MI, std::unique_ptr<C_MI>, PyC_MI>(m, "C_MI", py::base<B_MI>())
-        .def(py::init<>());
-    py::class_<D_MI, std::unique_ptr<D_MI>, PyD_MI>(m, "D_MI", py::base<C_MI>())
-        .def(py::init<>());
-
 };
 
 

example/example-virtual-functions.py

@@ -4,7 +4,7 @@ import sys
 sys.path.append('.')
 
 from example import ExampleVirt, runExampleVirt, runExampleVirtVirtual, runExampleVirtBool
-from example import A_Repeat, B_Repeat, C_Repeat, D_Repeat, A_MI, B_MI, C_MI, D_MI, A_Tpl, B_Tpl, C_Tpl, D_Tpl
+from example import A_Repeat, B_Repeat, C_Repeat, D_Repeat, A_Tpl, B_Tpl, C_Tpl, D_Tpl
 
 class ExtendedExampleVirt(ExampleVirt):
     def __init__(self, state):
@@ -40,11 +40,6 @@ sys.stdout.flush()
 class VI_AR(A_Repeat):
     def unlucky_number(self):
         return 99
-class VI_AMI(A_MI):
-    def unlucky_number(self):
-        return 990
-    def say_something(self, times):
-        return A_MI.say_something(self, 2*times)
 class VI_AT(A_Tpl):
     def unlucky_number(self):
         return 999
@@ -52,17 +47,11 @@ class VI_AT(A_Tpl):
 class VI_CR(C_Repeat):
     def lucky_number(self):
         return C_Repeat.lucky_number(self) + 1.25
-class VI_CMI(C_MI):
-    def lucky_number(self):
-        return 1.75
 class VI_CT(C_Tpl):
     pass
 class VI_CCR(VI_CR):
     def lucky_number(self):
         return VI_CR.lucky_number(self) * 10
-class VI_CCMI(VI_CMI):
-    def lucky_number(self):
-        return VI_CMI.lucky_number(self) * 100
 class VI_CCT(VI_CT):
     def lucky_number(self):
         return VI_CT.lucky_number(self) * 1000
@@ -73,11 +62,6 @@ class VI_DR(D_Repeat):
         return 123
     def lucky_number(self):
         return 42.0
-class VI_DMI(D_MI):
-    def unlucky_number(self):
-        return 1230
-    def lucky_number(self):
-        return -9.5
 class VI_DT(D_Tpl):
     def say_something(self, times):
         print("VI_DT says:" + (' quack' * times))
@@ -87,12 +71,12 @@ class VI_DT(D_Tpl):
         return -4.25
 
 classes = [
-    # A_Repeat, A_MI, A_Tpl, # abstract (they have a pure virtual unlucky_number)
-    VI_AR, VI_AMI, VI_AT,
-    B_Repeat, B_MI, B_Tpl,
-    C_Repeat, C_MI, C_Tpl,
-    VI_CR, VI_CMI, VI_CT, VI_CCR, VI_CCMI, VI_CCT,
-    D_Repeat, D_MI, D_Tpl, VI_DR, VI_DMI, VI_DT
+    # A_Repeat, A_Tpl, # abstract (they have a pure virtual unlucky_number)
+    VI_AR, VI_AT,
+    B_Repeat, B_Tpl,
+    C_Repeat, C_Tpl,
+    VI_CR, VI_CT, VI_CCR, VI_CCT,
+    D_Repeat, D_Tpl, VI_DR, VI_DT
 ]
 
 for cl in classes:

example/example-virtual-functions.ref

@@ -14,10 +14,6 @@ VI_AR:
 hihihi
 Unlucky = 99
 
-VI_AMI:
-hihihihihihi
-Unlucky = 990
-
 VI_AT:
 hihihi
 Unlucky = 999
@@ -27,11 +23,6 @@ B says hi 3 times
 Unlucky = 13
 Lucky = 7.00
 
-B_MI:
-B says hi 3 times
-Unlucky = 13
-Lucky = 7.00
-
 B_Tpl:
 B says hi 3 times
 Unlucky = 13
@@ -42,11 +33,6 @@ B says hi 3 times
 Unlucky = 4444
 Lucky = 888.00
 
-C_MI:
-B says hi 3 times
-Unlucky = 4444
-Lucky = 888.00
-
 C_Tpl:
 B says hi 3 times
 Unlucky = 4444
@@ -57,11 +43,6 @@ B says hi 3 times
 Unlucky = 4444
 Lucky = 889.25
 
-VI_CMI:
-B says hi 3 times
-Unlucky = 4444
-Lucky = 1.75
-
 VI_CT:
 B says hi 3 times
 Unlucky = 4444
@@ -72,11 +53,6 @@ B says hi 3 times
 Unlucky = 4444
 Lucky = 8892.50
 
-VI_CCMI:
-B says hi 3 times
-Unlucky = 4444
-Lucky = 175.00
-
 VI_CCT:
 B says hi 3 times
 Unlucky = 4444
@@ -87,11 +63,6 @@ B says hi 3 times
 Unlucky = 4444
 Lucky = 888.00
 
-D_MI:
-B says hi 3 times
-Unlucky = 4444
-Lucky = 888.00
-
 D_Tpl:
 B says hi 3 times
 Unlucky = 4444
@@ -102,11 +73,6 @@ B says hi 3 times
 Unlucky = 123
 Lucky = 42.00
 
-VI_DMI:
-B says hi 3 times
-Unlucky = 1230
-Lucky = -9.50
-
 VI_DT:
 VI_DT says: quack quack quack
 Unlucky = 1234