Fix py::trampoline_self_life_support visibility in docs (#5766)

C++ classes default inheritance rule is private.
I believe py::trampoline_self_life_support must be public to work correctly.

Author: gentlegiantJGC

docs/advanced/classes.rst

@@ -64,7 +64,7 @@ helper class that is defined as follows:
 
 .. code-block:: cpp
 
-    class PyAnimal : public Animal, py::trampoline_self_life_support {
+    class PyAnimal : public Animal, public py::trampoline_self_life_support {
     public:
         /* Inherit the constructors */
         using Animal::Animal;
@@ -262,13 +262,13 @@ override the ``name()`` method):
 
 .. code-block:: cpp
 
-    class PyAnimal : public Animal, py::trampoline_self_life_support {
+    class PyAnimal : public Animal, public py::trampoline_self_life_support {
     public:
         using Animal::Animal; // Inherit constructors
         std::string go(int n_times) override { PYBIND11_OVERRIDE_PURE(std::string, Animal, go, n_times); }
         std::string name() override { PYBIND11_OVERRIDE(std::string, Animal, name, ); }
     };
-    class PyDog : public Dog, py::trampoline_self_life_support {
+    class PyDog : public Dog, public py::trampoline_self_life_support {
     public:
         using Dog::Dog; // Inherit constructors
         std::string go(int n_times) override { PYBIND11_OVERRIDE(std::string, Dog, go, n_times); }
@@ -290,7 +290,7 @@ declare or override any virtual methods itself:
 .. code-block:: cpp
 
     class Husky : public Dog {};
-    class PyHusky : public Husky, py::trampoline_self_life_support {
+    class PyHusky : public Husky, public py::trampoline_self_life_support {
     public:
         using Husky::Husky; // Inherit constructors
         std::string go(int n_times) override { PYBIND11_OVERRIDE_PURE(std::string, Husky, go, n_times); }
@@ -306,14 +306,14 @@ follows:
 .. code-block:: cpp
 
     template <class AnimalBase = Animal>
-    class PyAnimal : public AnimalBase, py::trampoline_self_life_support {
+    class PyAnimal : public AnimalBase, public py::trampoline_self_life_support {
     public:
         using AnimalBase::AnimalBase; // Inherit constructors
         std::string go(int n_times) override { PYBIND11_OVERRIDE_PURE(std::string, AnimalBase, go, n_times); }
         std::string name() override { PYBIND11_OVERRIDE(std::string, AnimalBase, name, ); }
     };
     template <class DogBase = Dog>
-    class PyDog : public PyAnimal<DogBase>, py::trampoline_self_life_support {
+    class PyDog : public PyAnimal<DogBase>, public py::trampoline_self_life_support {
     public:
         using PyAnimal<DogBase>::PyAnimal; // Inherit constructors
         // Override PyAnimal's pure virtual go() with a non-pure one:
@@ -564,7 +564,7 @@ an alias:
         // ...
         virtual ~Example() = default;
     };
-    class PyExample : public Example, py::trampoline_self_life_support {
+    class PyExample : public Example, public py::trampoline_self_life_support {
     public:
         using Example::Example;
         PyExample(Example &&base) : Example(std::move(base)) {}
@@ -1170,7 +1170,7 @@ described trampoline:
         virtual int foo() const { return 42; }
     };
 
-    class Trampoline : public A, py::trampoline_self_life_support {
+    class Trampoline : public A, public py::trampoline_self_life_support {
     public:
         int foo() const override { PYBIND11_OVERRIDE(int, A, foo, ); }
     };

docs/advanced/misc.rst

@@ -80,7 +80,7 @@ could be realized as follows (important changes highlighted):
 .. code-block:: cpp
     :emphasize-lines: 8,30,31
 
-    class PyAnimal : public Animal, py::trampoline_self_life_support {
+    class PyAnimal : public Animal, public py::trampoline_self_life_support {
     public:
         /* Inherit the constructors */
         using Animal::Animal;