Consider the following
Dart Code
import 'dart:math';
void main() {
SomeClass someClass = new SomeClass();
Function pointer = ((new Random().nextInt(100) % 2) == 0 ? someClass.fooMethod : someClass.barMethod);
print('$pointer');
}
Output
Closure 'barMethod$0' of Instance of 'MyClass'
(dartpad here)
Question
Assuming SomeClass is immutable, how do I get this to instead print simply barMethod or fooMethod? (also acceptable would be SomeClass.barMethod or SomeClass.fooMethod)
You can accomplish this using reflection, although this can be expensive if you intend to run it in the browser with dart2js. This snippet works:
import 'dart:math' show Random;
import 'dart:mirrors';
void main() {
MyClass myClass = new MyClass();
// Rather than (x % 2 == 0) you could do x.isEven,
// but there's also Random.nextBool()
Function pointer = new Random().nextBool() ? myClass.foo : myClass.bar;
ClosureMirror cm = reflect(pointer) as ClosureMirror;
print(MirrorSystem.getName(cm.function.simpleName));
pointer();
}
class MyClass {
void foo() {}
void bar() {}
}
Related
I am working on Mono.Cecil codegen util, and I want to preform following operation:
Loop through types
If type contains X attribute:
- Add ITestInterface implementation (where ITestInterface has defined some methods)
// For reference
public interface ITestInterface
{
void Something();
int IntSomething();
}
// Expected result, if type contains X attribute:
// Before codegen:
[X]
public class CodeGenExample
{
}
// After codegen
[X]
public class CodeGenExample : ITestInterface
{
public void Something()
{
// some stuff
}
public int IntSomething()
{
// do some stuff
return 0;
}
}
I have seen that .NET Reflection has a AddInterfaceImplementation method (https://learn.microsoft.com/pl-pl/dotnet/api/system.reflection.emit.typebuilder.addinterfaceimplementation?view=net-5.0).
Is there a Mono.Cecil equivalent or a workaround for this & how to use it?
That can be achieved by:
Iterating over all types defined in the assembly
Checking which types have the attribute applied to
Injecting the methods.
As an example you can do something like:
using System.Linq;
using Mono.Cecil;
using Mono.Cecil.Cil;
namespace inject
{
interface IMyInterface
{
int Something();
}
class MarkerAttribute : Attribute {}
[Marker]
class Foo
{
}
class Program
{
static void Main(string[] args)
{
if (args.Length == 1)
{
using var a = AssemblyDefinition.ReadAssembly(typeof(Program).Assembly.Location);
var interfaceToImplement = a.MainModule.GetType("inject.IMyInterface");
foreach(var t in a.MainModule.Types)
{
if (t.HasCustomAttributes && t.CustomAttributes.Any(c => c.Constructor.DeclaringType.Name == "MarkerAttribute"))
{
System.Console.WriteLine($"Adding methods to : {t}");
var something = new MethodDefinition("Something", MethodAttributes.Public | MethodAttributes.HideBySig | MethodAttributes.NewSlot | MethodAttributes.Virtual, a.MainModule.TypeSystem.Int32);
something.Body = new Mono.Cecil.Cil.MethodBody(something);
var il = something.Body.GetILProcessor();
il.Emit(OpCodes.Ldc_I4, 42);
il.Emit(OpCodes.Ret);
t.Methods.Add(something);
// Add the interface.
t.Interfaces.Add(new InterfaceImplementation(interfaceToImplement));
var path = typeof(Program).Assembly.Location + ".new";
a.Write(path);
System.Console.WriteLine($"Modified version written to {path}");
}
}
}
else
{
object f = new Foo();
IMyInterface itf = (IMyInterface) f;
System.Console.WriteLine($"Something() == {itf.Something()}");
}
}
}
}
Another potential solution is to have the methods implemented in an internal class and copying over their method bodies.
As a side note, these are 2 online tools you can use to explore/learn more about CIL, Mono.Cecil, C#:
Sharplab.io
Cecilifier (disclaimer: I'm the author of this one)
That being said if you can use C# 9.0 you may be able to leverage the new Source Generators feature.
I have test application:
import 'dart:mirrors';
class A {
void eventHandlerInt(List<int> x){}
void eventHandlerBool(List<bool> x){}
}
void testMirrors(aFunction){
ClosureMirror mir = reflect(aFunction);
var param = mir.function.parameters.first;
//How to get the Type T of List<T> of the first param?
}
void main() {
var a = new A();
testMirrors(a.eventHandlerInt);
testMirrors(a.eventHandlerBool);
}
I would like to be able to find out what the generic type is of the first parameter of the method passed into testMirrors, so in the example above it would be int then bool. Is this even possible? if I inspect param the type property is null.
List<TypeMirror> types = mir.function.parameters.first.type.typeArguments;
param.forEach((e) => print(e.simpleName));
prints
Symbol("int")
Symbol("bool")
I am trying to use Rome for parsing some rss feeds. One of the rss feeds says
specifies 0.91 as the version and no custom xml namespace is defined but the entries still have a custom element in them. Can I use Rome to parse such custom tags without any defined namespace?
Thanks.
Yes. You need to write a custom parser to do it.
Let's say you want to handle the elements customString and customDate. Start by extending the Item class to store the custom elements.
package com.example;
import com.sun.syndication.feed.rss.Item;
import java.util.Date;
public class CustomItem extends Item {
private String _customString;
private Date _customDate;
public String getCustomString() {
return _customString;
}
public void setCustomString(String customString) {
_customString = customString;
}
public Date getCustomDate() {
return _customDate;
}
public void setCustomDate(Date customDate) {
_customDate = customDate;
}
}
Then write the parser. You also need to handle any standard elements you want to parse.
package com.example;
import com.example.CustomItem;
import com.sun.syndication.feed.rss.Item;
import com.sun.syndication.io.WireFeedParser;
import com.sun.syndication.io.impl.DateParser;
import com.sun.syndication.io.impl.RSS091UserlandParser;
import org.jdom.Element;
public class CustomParser extends RSS091UserlandParser implements WireFeedParser {
public CustomItem parseItem(Element rssRoot, Element eItem) {
CustomItem customItem = new CustomItem();
// Standard elements
Item standardItem = super.parseItem(rssRoot, eItem);
customItem.setTitle(standardItem.getTitle());
customItem.setDescription(standardItem.getDescription());
// Non-standard elements
Element e = eItem.getChild("customString", getRSSNamespace());
if (e != null) {
customItem.setCustomString(e.getText());
}
e = eItem.getChild("customDate", getRSSNamespace());
if (e != null) {
customItem.setCustomDate(DateParser.parseDate(e.getText()));
}
return customItem;
}
}
Finally you need to define your parser in a rome.properties file along with parsers for any other type of feed you want to handle.
# Feed Parser implementation classes
#
WireFeedParser.classes=com.example.CustomParser
You need to write a custom converter to get the data.
part of code same to above.
Start by extending the Item class to store the custom elements.
package com.example;
import com.sun.syndication.feed.rss.Item;
import java.util.Date;
public class CustomItem extends Item {
private String _customString;
private Date _customDate;
public String getCustomString() {
return _customString;
}
public void setCustomString(String customString) {
_customString = customString;
}
public Date getCustomDate() {
return _customDate;
}
public void setCustomDate(Date customDate) {
_customDate = customDate;
}
}
Then write the parser. You also need to handle any standard elements you want to parse.
package com.example;
import com.example.CustomItem;
import com.sun.syndication.feed.rss.Item;
import com.sun.syndication.io.WireFeedParser;
import com.sun.syndication.io.impl.DateParser;
import com.sun.syndication.io.impl.RSS091UserlandParser;
import org.jdom.Element;
public class CustomParser extends RSS091UserlandParser implements WireFeedParser {
public CustomItem parseItem(Element rssRoot, Element eItem) {
CustomItem customItem = new CustomItem();
// Standard elements
Item standardItem = super.parseItem(rssRoot, eItem);
customItem.setTitle(standardItem.getTitle());
customItem.setDescription(standardItem.getDescription());
// Non-standard elements
Element e = eItem.getChild("customString", getRSSNamespace());
if (e != null) {
customItem.setCustomString(e.getText());
}
e = eItem.getChild("customDate", getRSSNamespace());
if (e != null) {
customItem.setCustomDate(DateParser.parseDate(e.getText()));
}
return customItem;
}
}
Then write the converter.
public class CustomConverter extends ConverterForRSS20 {
protected SyndEntry createSyndEntry(Item item) {
List<HashMap<String,String>> temp = new ArrayList<HashMap<String,String>>();
SyndEntry syndEntry = super.createSyndEntry(item);
customItem customItem = (customItem)item;
List<String> customList = new ArrayList<String>();
customList.add( customItem.getCustomString() );
//set to empty attribute ex foreignmarkup
syndEntry.setForeignMarkup( customList );
return syndEntry;
}
}
Finally you need to define your parser in a rome.properties file along with parsers for any other type of feed you want to handle.
# Feed Parser implementation classes
#
WireFeedParser.classes=com.example.CustomParser
# Feed Converter implementation classes
#
Converter.classes=com.example.CustomConverter
Then you can get value.
SyndFeed feed = input.build(new XmlReader(feedUrl));
List<SyndEntryImpl> entrys = feed.getEntries();
for(SyndEntryImpl entry:entrys ){
System.out.println( entry.getForeignMarkup() );
}
I would like some help in casting a pointer to a C struct to a jna strucuture. I am using jna to receive a callback function from a dll, the function has a parameter that is a pointer to a C struct, when a I try to cast the pointer to a jna structure I get wrong structure values.
That is the C struct:
typedef struct
{
int x;
int y;
}Point;
Point *gpt;
typedef struct
{
int x;
int y;
Point pt1;
}Point2;
Point2 *gpt2;
That is the callback function in C with a pointer (void *params) to Point2 sctruct:
void __stdcall PointCallback(void *params, int param_size)
So, I've made this code in java to receive the callback and get the original struct:
// Point.java
package Callback.UsePointLib;
import com.sun.jna.Structure;
public class Point extends Structure
{
public static class ByValue extends Point implements Structure.ByValue {}
public int x;
public int y;
}
//Point2.java
package Callback.UsePointLib;
import com.sun.jna.Pointer;
import com.sun.jna.Structure;
public class Point2 extends Structure {
public int x;
public int y;
Point pt1;
public Point2(Pointer p){
super(p);
}
}
Callback implementation:
//UsePointLib.java
public interface IFuncCallback extends StdCallCallback{
void callback(Pointer Params, int ParamSize);
}
public class FuncCallback implements IFuncCallback{
#Override
public void callback(Pointer Params, int ParamSize) {
Point2 pt2; // = new Point2();
pt2 = new Point2(Params);
System.out.println("pt2.x = "+pt2.x); **<- I get zero here instead of four**
System.out.println("pt2.y = "+pt2.y); **<- I get zero here instead of five**
System.out.println("pt2.pt1.x = "+pt2.pt1.x);**<- pt1 is null, throwing exception**
System.out.println("pt2.pt1.y = "+pt2.pt1.y);**<- same as pt1.**
}
}
I've made a C program to access the dll and receive the callback and it works ok, it receives the correct values. So, the problem is my java code. I've tried many alternatives with no success.
Please, I'd appreciate any help on that.
Thanks,
Fernando.
EDIT
I've modified the code and it works partially.
//UsePointLib.java
public interface IFuncCallback extends StdCallCallback{
void callback(Pointer Params, int ParamSize);
}
public class FuncCallback implements IFuncCallback{
#Override
public void callback(Pointer Params, int ParamSize) {
Point2 pt2; // = new Point2();
pt2 = new Point2(Params);
*pt2.read();* **<--Modification**
System.out.println("pt2.x = "+pt2.x); **<- I get the correct value (four)**
System.out.println("pt2.y = "+pt2.y); **<- I get the correct value (five)**
System.out.println("pt2.pt1.x = "+pt2.pt1.x);**<- pt1 is still null, throwing exception**
System.out.println("pt2.pt1.y = "+pt2.pt1.y);**<- same as pt1.**
}
}
The jna docs say that the constructor Structure(Pointer) allocates a structure onto a preallocated memory. It wont automatically assign values for you.I don't think thats what you want.
Change the constructors to
public Point2(){
super();
}
public Point2(Point1 p){
super();
pt1.x = p.x;
pt1.y = p.y;
this.x = something;
this.y = something;
}
Within the context of a callback, JNA will automatically call Structure.read on entry and Structure.write on exit for any parameters of type Structure.
If you declare your callback method signature to use a Structure type of the appropriate subclass ("Point2" in your example), the copying to/from native memory should be automatic.
A.as :
public class A {
public function getFunction():Function {
return function():void {
if(this is C) {
trace("C");
} else {
trace("not C");
}
}
}
public function func1():void {
var internalFunc:Function = getFunction();
internalFunc();
}
}
B.as :
public class B extends A implements C {
}
In some other class :
var b:B = new B();
B.func1();
Output is :
"Not C"
I was expecting the trace output to be
"C"
Can someone explain why?
An anonymous function, if called directly, is scoped to the global object. If you trace this inside it, you will see [object global] instead of [object B], as you would, if this refered to b.
A common workaround is using a closure:
var self:A = this;
return function():void {
if(self is C) {
trace("C");
} else {
trace("not C");
}
}
Please note however, the instance-members of a class defining an anonymous function are available from within. This works, because they are resolved at compile time.
edit in response to Amarghosh's question:
Yes, this points to the global object, but that doesn't mean, you cannot access the instance members of the declaring class. This little piece of code should explain the details:
package {
import flash.display.Sprite;
public class Test extends Sprite {
private var foo:String = "foo";
public function Test() {
var anonymous:Function = function ():void {
trace(foo);//foo
trace(this.foo);//undefined
};
anonymous();
}
}
}
greetz
back2dos
A few things with the code that I assume are just typos?
The getFunction() method doesn't return anything and will thus cause a compiler error.
Your call code calls func1() as a static method, not as a method on an instance of the B. This will also cause a compiler error. I believe these are typos.
In my tests, using your modified code. The output is C. There must be something else going on with your code. Here are my mods to A:
public function getFunction():Function {
if(this is C) {
trace("C");
} else {
trace("not C");
}
return getFunction;
}
Here is my mod to the runnable code, which I put in creationComplete of an empty MXML Application file:
var b:B = new B();
b.func1();
I assume your "real world" code is more extensive than the sample and there must be something else going on.