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Macros to simplify usage of class template AttachedVirtualFunction ...

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... And allow correct linkage when overrides are defined in dynamically loaded
modules
This commit is contained in:
Paul Licameli
2020-10-25 13:42:41 -04:00
parent ed3e4de17b
commit 48217d5acf
18 changed files with 57 additions and 60 deletions
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52
libraries/lib-registries/AttachedVirtualFunction.h
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@@ -72,13 +72,15 @@ AttachedVirtualFunction<
AbstractHost, // class to be switched on by runtime type
int, double // other arguments
>;
// Allow correct linkage for overrides defined in dynamically loaded modules:
DECLARE_EXPORTED_ATTACHED_VIRTUAL(AUDACITY_DLL_API, DoSomething);
```
Definitions needed:
```
//file Client.cpp
// Define the default function body here (as a function returning a function!)
template<> auto DoSomething::Implementation() -> Function {
// Define the default function body here
DEFINE_ATTACHED_VIRTUAL(DoSomething) {
return [](AbstractHost &host, int arg1, double arg2) {
return ErrorCode::Ok;
};
@@ -86,9 +88,6 @@ template<> auto DoSomething::Implementation() -> Function {
// at runtime if the virtual function is invoked for a host subclass for which no override
// was defined.
}
// Must also guarantee construction of an instance of class DoSomething at least
// once before any use of DoSomething::Call()
static DoSomething registerMe;
```
Usage of the method somewhere else:
@@ -124,7 +123,7 @@ Overrides of the method, defined in any other .cpp file:
// An override of the function, building up a hierarchy of function bodies parallel
// to the host class hierarchy
using DoSomethingSpecial = DoSomething::Override< SpecialHost >;
template<> template<> auto DoSomethingSpecial::Implementation() -> Function {
DEFINE_ATTACHED_VIRTUAL_OVERRIDE(DoSomethingSpecial) {
// The function can be defined without casting the first argument
return [](SpecialHost &host, int arg1, double arg2) {
return arg1 == 0 ? ErrorCode::Ok : ErrorCode::Bad;
@@ -135,8 +134,7 @@ static DoSomethingSpecial registerMe;
// A further override, demonstrating call-through too
using DoSomethingExtraSpecial =
DoSomething::Override< ExtraSpecialHost, DoSomethingSpecial >;
template<> template<>
auto DoSomethingExtraSpecial::Implementation() -> Function {
DEFINE_ATTACHED_VIRTUAL_OVERRIDE(DoSomethingExtraSpecial) {
return [](ExtraSpecialHost &host, int arg1, double arg2){
// Call the immediately overridden version of the function
auto result = Callthrough( host, arg1, arg2 );
@@ -173,11 +171,7 @@ public:
//! At least one static instance must be created; more instances are harmless
/*! (There will be others if there are any overrides.) */
AttachedVirtualFunction()
{
static std::once_flag flag;
std::call_once( flag, []{ Register<This>( Implementation() ); } );
}
AttachedVirtualFunction();
//! For defining overrides of the method
/*!
@@ -280,11 +274,33 @@ private:
};
using Registry = std::vector< Entry >;
static Registry &GetRegistry()
{
static Registry registry;
return registry;
}
static Registry &GetRegistry();
};
//! Typically follow the `using` declaration of a new AttachedVirtualFunction with this macro
#define DECLARE_EXPORTED_ATTACHED_VIRTUAL(DECLSPEC, Name) \
template<> DECLSPEC Name::AttachedVirtualFunction(); \
template<> auto DECLSPEC Name::GetRegistry() -> Registry &; \
template<> auto DECLSPEC Name::Implementation() -> Function
//! Used in the companion .cpp file to the .h using the above macro; followed by a function body
#define DEFINE_ATTACHED_VIRTUAL(Name) \
template<> Name::AttachedVirtualFunction() \
{ \
static std::once_flag flag; \
std::call_once( flag, []{ Register<Object>( Implementation() ); } ); \
} \
template<> auto Name::GetRegistry() -> Registry & \
{ \
static Registry registry; \
return registry; \
} \
static Name register ## Name ; \
template<> auto Name::Implementation() -> Function
//! Used to define overriding function; followed by a function body
#define DEFINE_ATTACHED_VIRTUAL_OVERRIDE(Name) \
static Name register ## Name ; \
template<> template<> auto Name::Implementation() -> Function \
#endif