I'm writing a program using TypeScript. The problem is I implemented HTMLElement interface.
export class IEElement implements HTMLElement {
// something here
}
The compiler shows many errors that I have some properties missing (IEElement declares an interface but does not implement it). I have implemented about 5 properties that I need to. The rest is redundant. How to avoid errors? Do I need to implement all the interface members?
Yes, you need to implement all non-optional interface members.
The interface is a contract, if you have a class that implements that contract you are promising to implement everything in that contract.
The HTMLElement interface has a lot to implement - but if you just want to add a bit of behaviour, perhaps you could start with an existing implementation...
interface SpecialElement extends HTMLElement {
myCustomFunction: () => void;
}
var element = <SpecialElement>document.getElementById('example');
element.myCustomFunction = function () { };
Related
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'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.
It is possible to create simple annotation for GWT client which give me possibility to use on client side:
#NewAnnotation
myClass myObject
instead of:
myClass myObject=new myClass();
This is essentially the pattern used by UiBinder. The way to implement this behavior is to write a Generator that produces the glue code to assign values to the fields.
You would be able to write something like:
class MyClass {
#NewAnnotation
SomeType field;
interface MyFieldFiller extends FieldFiller<MyClass> {}
MyClass() {
GWT.create(MyFieldFiller.class).populate(this);
}
}
You might want to look at GIN instead, which already implements a very robust dependency-injection mechanism.
How do I register all the instances of a generic interface in Structured Map?
I know how to do this for a none generic interface:
internal class MVCDemoRegistry : Registry
{
public MVCDemoRegistry()
{
Scan(x =>
{
x.Assembly("MVCDemo");
x.Assembly("MVCDemo.Infrastructure");
x.Assembly("MVCDemo.Services");
x.AddAllTypesOf<ISupplyView>();
});
}
}
I would go with something like
// in IToaster.cs
public interface IToaster<T> {}
// in your StructureMap registry
Scan(x =>
{
x.Assembly("MVCDemo");
x.Assembly("MVCDemo.Infrastructure");
x.Assembly("MVCDemo.Services");
x.AddAllTypesOf(typeof(IToaster<>))
});
The key here is that this approach uses the non-generic overload of AddAllTypesOf(). Otherwise this becomes a sticky widget indeed.
See this SO thread for a good discussion around these concerns: StructureMap Auto registration for generic types using Scan
This should do the trick unless there's something about your approach I'm missing - feel free to update if so.