I'm trying to implement a class instance of an interface class. Exploring the interface (.NET DLL) with the project explorer, it says:
bool CreateInstance(SharedLibrary::MemoryArbiter^ pntMemory,
SharedLibrary::clsMessageQueue^ pntMessageQueue,
SharedLibrary::clsGPIO^ pntGPIO,
SharedLibrary::Types^ pntProgramSettings,
SharedLibrary::DisplayDriver^ pntDisplayDriver)
Member from Plugin_Interface::IPlugin
But if I write in my MyClass.h:
using namespace System;
using namespace System::ComponentModel;
using namespace SharedLibrary;
namespace MyCppPlugin {
[AttributeUsageAttribute(AttributeTargets::Class | AttributeTargets::Method |
AttributeTargets::Property | AttributeTargets::Field,
AllowMultiple = true, Inherited = false)]
ref class MyPlugin abstract : public Plugin_Interface::IPlugin
{
bool CreateInstance(SharedLibrary::MemoryArbiter^ pntMemory,
SharedLibrary::clsMessageQueue^ pntMessageQueue,
SharedLibrary::clsGPIO^ pntGPIO, SharedLibrary::Types^
pntProgramSettings, SharedLibrary::DisplayDriver^ pntDisplayDriver);
};
};
It says: "error C3766: Missing implementation of Plugin_Interface::IPlugin::CreateInstace(...)
What the heck do I do wrong?
EDIT:
Forgot the abstract statement.
And: Why is it saying "IntelliSense: Class can not implement interface member function "Plugin_Interface::IPlugin::CreateInstance" (declared in "Plugin_Interface.dll")"
???
You got a lot more diagnostic messages from this snippet, you are making several mistakes:
[AttributeUsage] is only valid on a class that derives from System::Attribute. You no doubt need to use some kind of attribute so that the plugin host can recognize your class as a valid plugin candidate, I can't guess what that attribute might be.
A method that implements an interface method should be public.
A method that implements an interface method must be virtual.
The method signature must be an exact match with the interface method declaration.
Just in case: you must actually implement the method, not just declare it.
The third and forth bullets are the chief reasons for the "must provide an implementation of the interface method" compile error. So proper code ought to resemble something like this:
[NoIdeaWhatAttribute]
public ref class MyPlugin : public Plugin_Interface::IPlugin {
public:
virtual bool CreateInstance(SharedLibrary::MemoryArbiter^% pntMemory,
SharedLibrary::clsMessageQueue^% pntMessageQueue,
SharedLibrary::clsGPIO^% pntGPIO,
SharedLibrary::Types^% pntProgramSettings,
SharedLibrary::DisplayDriver^% pntDisplayDriver)
{
// Todo...
return false;
}
};
I got it. Thanks to Hans Passant who gave me so many hints :)
To export the function it has to implement the Interface 1:1. The export statement has to be added over the class header:
[Export(IPlugin::typeid)]
public ref class MyPlugin : public Plugin_Interface::IPlugin
And: While VB.NET will compile to "Any CPU" and C++/CLI will compile to Win64/Win32 it will missfit. Both Projects have to have the same target - either 64bit OR 32bit.
Now it works.
Related
Often people ask AspectJ questions like this one, so I want to answer it in a place I can easily link to later.
I have this marker annotation:
package de.scrum_master.app;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
#Inherited
#Retention(RetentionPolicy.RUNTIME)
public #interface Marker {}
Now I annotate an interface and/or methods like this:
package de.scrum_master.app;
#Marker
public interface MyInterface {
void one();
#Marker void two();
}
Here is a little driver application which also implements the interface:
package de.scrum_master.app;
public class Application implements MyInterface {
#Override
public void one() {}
#Override
public void two() {}
public static void main(String[] args) {
Application application = new Application();
application.one();
application.two();
}
}
Now when I define this aspect, I expect that it gets triggered
for each constructor execution of an annotated class and
for each execution of an annotated method.
package de.scrum_master.aspect;
import de.scrum_master.app.Marker;
public aspect MarkerAnnotationInterceptor {
after() : execution((#Marker *).new(..)) && !within(MarkerAnnotationInterceptor) {
System.out.println(thisJoinPoint);
}
after() : execution(#Marker * *(..)) && !within(MarkerAnnotationInterceptor) {
System.out.println(thisJoinPoint);
}
}
Unfortunately the aspect prints nothing, just as if class Application and method two() did not have any #Marker annotation. Why does AspectJ not intercept them?
The problem here is not AspectJ but the JVM. In Java, annotations on
interfaces,
methods or
other annotations
are never inherited by
implementing classes,
overriding methods or
classes using annotated annotations.
Annotation inheritance only works from classes to subclasses, but only if the annotation type used in the superclass bears the meta annotation #Inherited, see JDK JavaDoc.
AspectJ is a JVM language and thus works within the JVM's limitations. There is no general solution for this problem, but for specific interfaces or methods you wish to emulate annotation inheritance for, you can use a workaround like this:
package de.scrum_master.aspect;
import de.scrum_master.app.Marker;
import de.scrum_master.app.MyInterface;
/**
* It is a known JVM limitation that annotations are never inherited from interface
* to implementing class or from method to overriding method, see explanation in
* JDK API.
* <p>
* Here is a little AspectJ trick which does it manually.
*
*/
public aspect MarkerAnnotationInheritor {
// Implementing classes should inherit marker annotation
declare #type: MyInterface+ : #Marker;
// Overriding methods 'two' should inherit marker annotation
declare #method : void MyInterface+.two() : #Marker;
}
Please note: With this aspect in place, you can remove the (literal) annotations from the interface and from the annotated method because AspectJ's ITD (inter-type definition) mechanics adds them back to the interface plus to all implementing/overriding classes/methods.
Now the console log when running the Application says:
execution(de.scrum_master.app.Application())
execution(void de.scrum_master.app.Application.two())
By the way, you could also embed the aspect right into the interface so as to have everything in one place. Just be careful to rename MyInterface.java to MyInterface.aj in order to help the AspectJ compiler to recognise that it has to do some work here.
package de.scrum_master.app;
public interface MyInterface {
void one();
void two();
// Cannot omit 'static' here due to https://bugs.eclipse.org/bugs/show_bug.cgi?id=571104
public static aspect MarkerAnnotationInheritor {
// Implementing classes should inherit marker annotation
declare #type: MyInterface+ : #Marker;
// Overriding methods 'two' should inherit marker annotation
declare #method : void MyInterface+.two() : #Marker;
}
}
Update 2021-02-11: Someone suggested an edit to the latter solution, saying that the aspect MarkerAnnotationInheritor nested inside interface MyInterface is implicitly public static, so the modifiers in the aspect declaration could be omitted. In principle this is true, because members (methods, nested classes) of interfaces are always public by default and a non-static inner class definition would not make sense inside an interface either (there is no instance to bind it to). I like to be explicit in my sample code, though, because not all Java developers might know these details.
Furthermore, currently the AspectJ compiler in version 1.9.6 throws an error if we omit static. I have just created AspectJ issue #571104 for this problem.
I have a common interface that describes access to the output stream like this:
interface IOutput {
function writeInteger(aValue:Int):Void;
}
And I have an abstract implementation of this interface based on standard haxe.io.BytesOutput class:
abstract COutput(BytesOutput) from BytesOutput {
public inline function new(aData:BytesOutput) {
this = aData;
}
public inline function writeInteger(aValue:Int):Void {
this.writeInt32(aValue);
}
}
Though this abstract is truly implementing interface described above there's no direct reference to interface and when I'm trying to use it like this:
class Main {
public static function out(aOutput:IOutput) {
aOutput.writeInteger(0);
}
public static function main() {
var output:COutput = new BytesOutput();
out(output); // type error
}
}
Compiler throws an error: COutput should be IOutput. I can solve this problem only through using common class that wraps BytesOutput and implements IOutput.
My question is how to show the Haxe compiler that the abstract implements the interface.
Abstracts can't implement interfaces because they're a compile-time feature and don't exist at runtime. This conflicts with interfaces, they do exist at runtime and dynamic runtime checks like Std.is(something, IOutput) have to work.
Haxe also has a mechanism called structural subtyping that can be used as an alternative to interfaces. With this approach, there's no need for an explicit implements declaration, it's good enough if something unifies with a structure:
typedef IOutput = {
function writeInteger(aValue:Int):Void;
}
Unfortunately, abstracts aren't compatible with structural subtyping either due to the way they're implemented.
Have you considered using static extensions instead? At least for your simple example, that seems like the perfect solution for making a writeInteger() method available for any haxe.io.Output:
import haxe.io.Output;
import haxe.io.BytesOutput;
using Main.OutputExtensions;
class Main {
static function main() {
var output = new BytesOutput();
output.writeInteger(0);
}
}
class OutputExtensions {
public static function writeInteger(output:Output, value:Int):Void {
output.writeInt32(value);
}
}
You could even combine this with structural subtyping so writeInteger() becomes available on anything that has a writeInt32() method (try.haxe link):
typedef Int32Writable = {
function writeInt32(value:Int):Void;
}
As #Gama11 states, abstracts cannot implement interfaces. In Haxe, for type to implement an interface, it must be able to be compiled to something class-like that can be called using the interface’s methods without any magic happening. That is, to use a type as its interface, there needs to be a “real” class implementing that type. Abstracts in Haxe compile down to their base type—the abstract itself is entirely invisible after compilation happens. Thus, at runtime, there is no instance of a class with the methods defined in your abstract which implement the interface.
However, you can make your abstract appear to implement an interface by defining an implicit conversion to the interface you are trying to implement. For your example, the following might work:
interface IOutput {
function writeInteger(aValue:Int):Void;
}
abstract COutput(BytesOutput) from BytesOutput {
public inline function new(aData:BytesOutput) {
this = aData;
}
#:to()
public inline function toIOutput():IOutput {
return new COutputWrapper((cast this : COutput));
}
public inline function writeInteger(aValue:Int):Void {
this.writeInt32(aValue);
}
}
class COutputWrapper implements IOutput {
var cOutput(default, null):COutput;
public function new(cOutput) {
this.cOutput = cOutput;
}
public function writeInteger(aValue:Int) {
cOutput.writeInteger(aValue);
}
}
class Main {
public static function out(aOutput:IOutput) {
aOutput.writeInteger(0);
}
public static function main() {
var output:COutput = new BytesOutput();
out(output);
out(output);
}
}
Run on try.haxe.org
Note that, each time an implicit conversion happens, a new instance of the wrapper will be constructed. This may have performance implications. If you only access your value through its interface, consider setting the type of your variable to the interface rather than the abstract.
This is similar to “boxing” a primitive/value type in C#. In C#, value types, defined using the struct keyword, are allowed to implement interfaces. Like an abstract in Haxe, a value type in C# is compiled (by the JITter) into untyped code which simply directly accesses and manipulates the value for certain operations. However, C# allows structs to implement interfaces. The C# compiler will translate any attempt to implicitly cast a struct to an implemented interface into the construction of a wrapper class which stores a copy of the value and implements the interface—similar to our manually authored wrapper class (this wrapper class is actually generated by the runtime as part of JITing and is performed by the IL box instruction. See M() in this example). It is conceivable that Haxe could add a feature to automatically generate such a wrapper class for you like C# does for struct types, but that is not currently a feature. You may, however, do it yourself, as exemplified above.
How do I create a template that each time when I create a class that extends MyClass, it will automatically add 3 functions.
EDIT:
In other words I am trying to implement Abstract functionality in AS3. Assume that MyClass have both private and protected methods.
I see the only way to write own code template and call it every time you need, in Flash Builder: window->preference->flash builder->editors->code template->action script->new and give the name to the template, for instance myclass.
You can use existed templates as an example for template syntax.
Template code for MyClass child class with three methods:
import my.package.MyClass
/**
* #author ${user}
*/
public class ${enclosing_type} extends MyClass
{
public function ${enclosing_type}()
{
}
override public function publicMethod():void
{
}
override protected function protectedMethod():void
{
}
override private function privateMethod():void
{
}
${cursor}
}
Usage:
Create new "action script file" or "new class",
remove all file content
type myclass and choose from auto-complete options template myclass
If you are actually extending MyClass, all of MyClass's functions are already available to your descendants. You can also override either of them with old header and desired new body, and still be able to call older versions of those functions via super qualifier. So, you add those functions to MyClass and let them be.
Another way is to make an interface - it's a set of declarations without any function bodies, which you have to implement in any class that wants this interface in its content. A short introduction to interfaces. Then your MyClass will be an interface, with 3 function declarations in it, and whichever class will be declared as implements MyClass will have to provide bodies for these functions.
Check other keywords on that page, including extends and implements.
Hope this helps.
EDIT: There are no abstract classes in AS3, however you can emulate abstract functions in a normal class via exception throwing:
protected function abstractFunction(...params):void {
throw new Error("Abstract!");
}
I have C++ code (not mine, so it is not editable). Problem is with extending protected functions and class.
#include "ExtraClass.h"
...
MyClass::MyClass()
{
...
protected:
bool Func{}
ExtraClass m_Foo;
...
}
I need access in Python to m_Foo methods and protected functions like Func() like
from MyClass import *
bar = MyClass()
bar.m_Foo.Run() //something like this
but have an compiler error:
*error: ‘ExtraClass MyApp::m_Foo’ is protected*
PS. If I change protected with public (just for try). I can access *m_Foo* only in readonly mode:
class_<MyClass>("MyClass", init<>())
.def_readonly("m_Foo", &MyClass::m_Foo)
Changing to *def_readwrite* went to compiler error:
/boost_1_52_0/boost/python/data_members.hpp:64:11: error: no match for ‘operator=’ in ‘(((ExtraClass)c) + ((sizetype)((const boost::python::detail::member<ExtraClass, MyClass>*)this)->boost::python::detail::member<ExtraClass, MyClass>::m_which)) = d’
Thank you for any help!
In general, if you want to wrap protected members, then you need to derive a (wrapper) class from the parent that makes the members public. (You can simply say using Base::ProtectedMember in a public section to expose it instead of wrapping it). You will then have wrap it normally. Like this:
class MyWrapperClass : public MyClass {
public:
using MyClass::m_Foo;
};
In this particular example (which is really not fully baked), if you want to access m_Foo, then you need to wrap ExtraClass. Assuming that you have The problem with readwrite is likely the implementation of ExtraClass (which probably doesn't supply a operator= that you can use).
I'm loading a .NET assembly dinamically via reflection and I'm getting all the classes that it contains (at the moment one). After this, I'm trying to cast the class to an interface that I'm 100% sure the class implements but I receive this exception: Unable to cast object of type System.RuntimeType to the type MyInterface
MyDLL.dll
public interface MyInterface
{
void MyMethod();
}
MyOtherDLL.dll
public class MyClass : MyInterface
{
public void MyMethod()
{
...
}
}
public class MyLoader
{
Assembly myAssembly = Assembly.LoadFile("MyDLL.dll");
IEnumerable<Type> types = extension.GetTypes().Where(x => x.IsClass);
foreach (Type type in types)
{
((MyInterface)type).MyMethod();
}
}
I have stripped out all the code that is not necessary. This is basically what I do. I saw in this question that Andi answered with a problem that seems the same mine but I cannot anyway fix it.
You are trying to cast a .NET framework object of type Type to an interface that you created. The Type object does not implement your interface, so it can't be cast. You should first create a specific instance of your object, such as through using an Activator like this:
// this goes inside your for loop
MyInterface myInterface = (MyInterface)Activator.CreateInstance(type, false);
myInterface.MyMethod();
The CreateInstance method has other overloades that may fit your needs.