SAM conversion of inlined lambda expression

[Thomas Jung]

I've checked if the current prototype solves the problem and it does not:

Function<Integer, Integer> a = Functions.compose(#(x){ x * x }, #(x){ x / 3 });

operator * cannot be applied to Object,Object
		Functions.compose(#(x){ x * x }, #(x){ x / 3 });

It works with the explicit type:
Function<Integer, Integer> a = Functions.compose(#(Integer x){ x * x
}, #(x){ x / 3 });

Thomas


On 7 August 2010 19:24, maurizio cimadamore
<maurizio.cimadamore at oracle.com> wrote:
> On 07/08/2010 15:57, Thomas Jung wrote:
>>
>> Hi Rémi,
>>
>> you're right. Defining
>>
>> public static<A,B,C>  Function<A,C>  simpleCompose(Function<B,C>  g,
>> Function<A, B>  f){
>>     return Functions.compose(g,f);
>> }
>> Function<String, String>  c = simpleCompose(#(x){ "a" + x }, #(x){ x + "b"
>> });
>>
>> works. Is there is way to get some debugging information of the type
>> inferencer?
>>
>> Thomas
>>
>
> Hi
> as Remi pointed out in an earlier email, there's a bug when the target
> method of a SAM conversion has a wildcard in return type position. Wildcards
> in argument types work w/o problems - a fix for this problem will be
> available soon.
>
> Thanks
> Maurizio
>>
>> On 7 August 2010 15:16, Rémi Forax<forax at univ-mlv.fr>  wrote:
>>
>>>
>>>  Le 07/08/2010 09:58, Thomas Jung a écrit :
>>>
>>>>
>>>> Hi,
>>>>
>>>> I'm playing a bit with the prototype (i.e. I've not read the specs in
>>>> full) and I'm puzzled after my second step.
>>>>
>>>> The initial code that uses Function
>>>>
>>>> (http://guava-libraries.googlecode.com/svn/trunk/javadoc/com/google/common/base/Function.html)
>>>> is:
>>>>
>>>> Function<String, String>    a = #(x){ "a" + x };
>>>> Function<String, String>    b = #(x){ x + "b" };
>>>> assertEquals("axb", Functions.compose(a, b).apply("x"));
>>>>
>>>> This works with type inference and does the conversion to the type
>>>> Function<F,T>. But if I inline the lambda expression it won't convert
>>>> them.
>>>>
>>>> Function<String, String>    c = Functions.<String, String>
>>>> compose(#(String x){ "a" + x }, #(String x){ x + "b" });
>>>>
>>>> I've added all type annotations to rule out that this is the problem.
>>>> The error message is:
>>>> "method compose in class Functions cannot be applied to given types".
>>>> (Can I get more information here about the types/problem?)
>>>>
>>>> Is this not supported?
>>>>
>>>> Thomas
>>>>
>>>>
>>>
>>> This is a bug, the prototype have a problem to infer types
>>> if there is a wilcard in the middle.
>>>
>>> by example, this doesn't compile:
>>> Function<String, ? extends String>  b = #(x){ x + "b" };
>>>
>>> So you can't use compose which is declared:|*
>>> *|<A,B,C>
>>>
>>> <../../../../com/google/common/base/Functions.html#compose%28com.google.common.base.Function,%20com.google.common.base.Function%29>Function
>>> <../../../../com/google/common/base/Function.html><A,C>  |compose
>>>
>>> <../../../../com/google/common/base/Functions.html#compose%28com.google.common.base.Function,%20com.google.common.base.Function%29>(Function
>>> <../../../../com/google/common/base/Function.html><B,C>  g, Function
>>> <../../../../com/google/common/base/Function.html><A,*? extends* B>  f)|
>>>
>>> Rémi
>>>
>>>
>>>
>>>
>>>
>>
>>
>
>