On Apr 20, 2011, at 6:16 PM, Jian Li wrote:
> Hi,
>
> I've just found a problem in our generated code for handling optional
> parameters. Suppose we define a method with optional parameter in numeric
> type, like the following in IDL:
> Foo bar(in [Optional] long long start, in [Optional] long long end);
>
> And we declare our C++ method as the following. Note that the default value
> of the 2nd parameter is not 0.
> PassRefPtr<Foo> bar(long long start = 0, long long end =
> std::numeric_limits<long long>::max());
>
> If we call the JS method with only 1 parameter, everything works as expected.
> However, if we call the JS method with 2 parameters and pass 'undefined' as
> the 2nd parameter, we trigger the problem.
Is it actually a bug that explicitly passing undefined acts like passing 0,
instead of like an omitted parameter? I think it's correct per Web IDL. What's
the specific case where this is a problem?
Regards,
Maciej
>
> By looking into the generated JSC code below, I found out that we are
> converting undefined JS value to 0 and pass it to the function. As the
> result, the default parameter value in the declaration is not respected.
> EncodedJSValue JSC_HOST_CALL jsFooPrototypeFunctionFoo(ExecState* exec)
> {
>
> JSValue thisValue = exec->hostThisValue();
> if (!thisValue.inherits(&JSFoo::s_info))
> return throwVMTypeError(exec);
> JSFoo* castedThis = static_cast<JSFoo*>(asObject(thisValue));
> Foo* imp = static_cast<Foo*>(castedThis->impl());
>
> int argsCount = exec->argumentCount();
> if (argsCount <= 0) {
> JSC::JSValue result = toJS(exec, castedThis->globalObject(),
> WTF::getPtr(imp->bar()));
> return JSValue::encode(result);
> }
>
> long long start(static_cast<long
> long>(exec->argument(0).toInteger(exec)));
> if (exec->hadException())
> return JSValue::encode(jsUndefined());
> if (argsCount <= 1) {
> JSC::JSValue result = toJS(exec, castedThis->globalObject(),
> WTF::getPtr(imp->bar(start)));
> return JSValue::encode(result);
> }
>
> long long end(static_cast<long long>(exec->argument(1).toInteger(exec)));
> if (exec->hadException())
> return JSValue::encode(jsUndefined());
>
> JSC::JSValue result = toJS(exec, castedThis->globalObject(),
> WTF::getPtr(imp->bar(start, end)));
> return JSValue::encode(result);
> }
>
> One solution is to add the default value support in IDL. For example, we can
> change the above definition of bar to something like:
> Foo bar(in [Optional, DefaultValue=0] long long start, in [Optional,
> DefaultValue=2147483647] long long end);
>
> Or the other way is to add a bool parameter for each optional parameter in
> the class method declaration, that is used to indicate if the passing
> parameter is defined or not. This would involve the change to both code
> generator scripts and the existing implementations.
>
> How do you think? Personally I like the 1st approach since it is simpler.
>
> Thanks,
>
> Jian
>
>
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