[Laszlo-dev] Re: [Laszlo-user] Interface support

[Oliver Steele]

This is one of the most often-requested features.

Here's what it would take to do it.  This is pseudocode, not a patch  
file or anything; someone would have to take this and run with it to  
make it happen.

Add an entry to lzx.rnc:
   interface = element interface {
     element method { nameAttribute }
   }

Add this line to the definition of toplevelElements in lzx.rnc:
   & interface

Allow 'extends' in <class> tags (again, in lzx.rnc):
      attribute extends {token}? &
   +  attribute implements {string}? &

Add new file org/openlaszlo/compiler/InterfaceDefinition.java:
   public class InterfaceDefinition {
     private final String mName;
     // List<String>
     private final List mMethodNames = new Vector();
     ...constructor...
     public void addMethod(String name) {...}
     public List getMethods() {return mMethodNames;}
   }

Add a field and accessors to ViewSchema.java:
   /// Map<String, InterfaceDefinition>
   private final Map mInterfaces = new HashMap();
   public void addInterface(InterfaceDefinition id) {...}
   public InterfaceDefinition getInterface() {...}

Add a new class InterfaceCompiler.java:
   public class InterfaceCompiler {
     static boolean isElement(Element element) {
         return element.tagName().equals("interface");
     }
     public InterfaceCompiler(CompilationEnvironment env) {super(env);}
     public void compile(Element element) {
       InterfaceDefinition id = new InterfaceDefinition();
       for each (Element method in element.getChildren("method"))
         id.addMethod(method.getAttribute("name"));
       env.getSchema().addInterface(def);
     }
   }

Add this line to Compiler.getElementCompiler:
         } else if (InterfaceCompiler.isElement(element)) {
             return new InterfaceCompiler(env);

And, finally, the tricky part.  Something like this in  
ClassCompiler.compile():
   String implements = element.getAttribute("implements");
   if (implements != null) {
     Set inheritedMethods = model.getInheritedMethods();
     Set undefinedMethods = new HashSet();
     for (String interfaceName in implements.tokenize()) {
       InterfaceDefinition id = env.getSchema().getInterface 
(interfaceName);
       if (id == null) {
         env.addWarning(...);
         continue;
       }
       for (String methodName in id.getMethodNames())
         if (!inheritedMethods.contains(methodName))
           undefinedMethods.add(methodName " in " interfaceName)
      if (!undefinedMethods.empty())
       env.addWarning(name + " doesn't implement " + ListUtils.format 
(undefinedMethods)));
    }
   }

And you need to write ClassModel.getInheritedMethods():
   protected Set getInheritedMethods() {
     Set methods = new HashSet();
     addInheritedMethodsTo(methods);
   }
   protected void addInheritedMethodsTo(Set methods) {
     methods.addAll(self.methods);
     if (superClass != null)
       superClass.addInheritedMethodsTo(methods);
   }

And some test cases for inheriting from one interface and two  
interfaces, and the error cases:
- name of the interface isn't valid
- two interfaces have the same names
- <interface> contains a tag that isn't <method>
- <method> doesn't have a @name attribute.
- method/@name isn't valid
- class/@implements isn't valid

This doesn't allow an interface to declare the number of parameters,  
or attributes, but that could be an extension later --- this keeps it  
simple.

Does this look reasonable?

On Jun 13, 2005, at 11:04 AM, kenly browne wrote:
> hey..good day
>
> I just want to know that is it possible in the future
> that laszlo might support interfaces..
>
> eg.. <interface name="support">
>        <method name="laszloDevelopers"/>
>        <method name="pleaseImplement"/>
>      </interface>
>
> I'm comming from a flex background and that made the
> coding real powerfull.
>
> Thanks for the time
>
> K,Browne
> Developer
>
>
>
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