Fwd: jsinterop woes: Part 1: instanceof function in generics casting

[Vassilis Virvilis]

Originally posted in gwt-users.

Two questions:

1. Do you want me to report it as a bug somewhere? and where that would be?
2. I have two more. Do you want me to post them here or this is not the right place to post at all?

---------- Forwarded message ----------
From: Vassilis Virvilis <vas...@gmail.com>
Date: Fri, Feb 24, 2017 at 2:26 PM
Subject: jsinterop woes: Part 1: instanceof function in generics casting
To: google-web-toolkit@googlegroups.com

Hi,

again I don't know if this is a bug but it hurts my style

D3 defines d3.scale.ordinal as both a function and an object. $wnd.d3.scale.ordinal returns function() in the browser's console though

   @JsType(isNative = true, name = "ordinal")
      public static class Ordinal {
           /** @todo TODO: this crashes. Why? */
           public native <I, O> O range(I[] values);       // this doesn't work
           //public native <I> Ordinal range(I[] values); // this works
      }

I want the generic type because then I can put it in a base class and share some code.

I am using it like this

D3.Scale.Ordinal color = D3.Scale.ordinal().range(new String[] {"#98abc5", "#8a89a6"});

Here is the javascript exception:

Error: java.lang.ClassCastException
    at java_lang_ClassCastException_ClassCastException__V.java_lang_Throwable_createError__Ljava_lang_String_2Ljava_lang_Object_2 [as package_private$java_lang$createError__Ljava_lang_String_2Ljava_lang_Object_2] (dashboard-0.js:7245)
    at java_lang_ClassCastException_ClassCastException__V.java_lang_Throwable_initializeBackingError__V [as private$java_lang_Throwable$initializeBackingError__V] (dashboard-0.js:7300)
    at java_lang_ClassCastException_ClassCastException__V.java_lang_Throwable_Throwable__V (dashboard-0.js:7133)
    at java_lang_ClassCastException_ClassCastException__V.java_lang_Exception_Exception__V (dashboard-0.js:7381)
    at java_lang_ClassCastException_ClassCastException__V.java_lang_RuntimeException_RuntimeException__V (dashboard-0.js:29724)
    at java_lang_ClassCastException_ClassCastException__V (dashboard-0.js:57274)
    at javaemul_internal_InternalPreconditions_checkCriticalType__ZV (dashboard-0.js:72135)
    at javaemul_internal_InternalPreconditions_checkType__ZV (dashboard-0.js:72342)
    at com_google_gwt_lang_Cast_castToNative__Ljava_lang_Object_2Lcom_google_gwt_core_client_JavaScriptObject_2Ljava_lang_Object_2 (dashboard-0.js:707)   

In

function com_google_gwt_lang_Cast_castToNative__Ljava_lang_Object_2Lcom_google_gwt_core_client_JavaScriptObject_2Ljava_lang_Object_2(src_0, jsType){
  com_google_gwt_lang_Cast_$clinit__V();
  javaemul_internal_InternalPreconditions_checkType__ZV(com_google_gwt_lang_Cast_jsEquals__Ljava_lang_Object_2Ljava_lang_Object_2Z(src_0, null) || com_google_gwt_lang_Cast_jsinstanceOf__Ljava_lang_Object_2Lcom_google_gwt_core_client_JavaScriptObject_2Z(src_0, jsType));
  return src_0;
}

Arguments:

• src_0:
• passed:
• evaluated: function scale(x)
• jsType:
• passed: $wnd.scale.ordinal
• evaluated: function anonymous()

The reason it fails is that

function com_google_gwt_lang_Cast_jsinstanceOf__Ljava_lang_Object_2Lcom_google_gwt_core_client_JavaScriptObject_2Z(obj, jsType){
  com_google_gwt_lang_Cast_$clinit__V();
  return obj && (jsType && obj instanceof jsType);
}

obj is src_0 != null and jsType = function anonymous() != null but (obj instanceof jsType) === false

Any idea about that?

--

Vassilis Virvilis

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Vassilis Virvilis

[Roberto Lublinerman]

The declaration 

  package somepackage;

  @JsNative(isTrue, name = "ordinal") 

  class Ordinal {

  ....

  }

effectively says that there is a native type "somepackage.ordinal", which d3.ordinal is not.

You can model it as a native interface for example where there is not such expectation.

So as I understand your report this is not a bug but just an error in modellin

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[Vassilis Virvilis]

Ηι,

thanks for answering

d3.ordinal does not exist as you said. However d3.scale.ordinal exists and that part works great.

in d3 ordinal is both a function ordinal() which returns an ordinal instance and an object with more methods such as range() which is the crux of my issue.

The problem there is that

• public native <I, O> O range(I[] values);       // this doesn't work

• // public native <I> Ordinal range(I[] values); // this works

I would like to use the first definition because it allows reusing some code between different scales. Otherwise I have to copy-paste the range() method multiple times instead of put it in a base class.

The problem is on the exceptions generated by the attempting casting.

As you said this may not be a bug but not for the reason you mentioned.

So the question remains: Should I report it as an issue?

   Vassilis

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Vassilis Virvilis

[Thomas Broyer]

On Sunday, June 25, 2017 at 1:24:40 PM UTC+2, Vassilis Virvilis wrote:

Ηι,

thanks for answering

d3.ordinal does not exist as you said. However d3.scale.ordinal exists and that part works great.

But it is not a type, so you cannot use 'instanceof' on it.

 

in d3 ordinal is both a function ordinal() which returns an ordinal instance and an object with more methods such as range() which is the crux of my issue.

The problem there is that

• public native <I, O> O range(I[] values);       // this doesn't work
• // public native <I> Ordinal range(I[] values); // this works

I would like to use the first definition because it allows reusing some code between different scales. Otherwise I have to copy-paste the range() method multiple times instead of put it in a base class.

In Java, generics are more or less syntactic sugar for using the erased type and casting values. So when using the first one, GWT will, when used with O==Ordinal, generate a cast from Object to Ordinal, which IIUC is what's causing the error, because your JsType is not a type that can be checked (a cast is translated in JS to a type-check using 'instanceof').

 

The problem is on the exceptions generated by the attempting casting.

As you said this may not be a bug but not for the reason you mentioned.

So the question remains: Should I report it as an issue?

I would say no. Your @JsType is wrong. You should either use an interface with @JsType(isNative=true, name="?", namespace=JsPackage.GLOBAL), or if you want to use fields use a class with @JsType(isNative=true, name="Object", namespace=JsPackage.GLOBAL) 

[Vassilis Virvilis]

Hm...

For me this d3 ordinal thing like implementing the () operator in c++. Is it a function with members and methods or is it an object with the ability to be called as a function?

Anyway if you and Roberto say it is not a bug then it's not a bug.

When I revisit my D3 bindings I will explore your proposals - but AFAIK there is no easy solution that resembles the original javascript API. Currently I prefer to copy paste among the inheritance pyramid (there are 2 or 3 subtypes) and have a create() method instead of ordinal() that generates the object.

If there is no objection I will post another stumbling block I encountered in my jsinterop journey.

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Vassilis Virvilis

[Vassilis Virvilis]

 I was not remembering correctly and my last comment was off. I am not using a create() method. So the editorial correction is

 s/and have a create() method instead of ordinal() that generates the object//g

 

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Vassilis Virvilis

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Vassilis Virvilis