Autoboxing vs wildcards

[Mark Mahieu]

Ah, of course - thanks for pointing that out!

On 23 May 2008, at 04:02, Neal Gafter wrote:

> Offhand, I'd say this should probably compile.  I'll look at it.   
> You can always resort to explicit type arguments as a workaround,  
> e.g. Reduce.<Integer>reduce(...).
>
> On Thu, May 22, 2008 at 5:45 PM, Mark Mahieu  
> <mark at twistedbanana.demon.co.uk> wrote:
> This class looks like it could compile to me, but the third call to  
> the 'reduce' method isn't considered valid unless I remove the  
> wildcard from the method's signature, but of course that then means  
> that the first call won't compile.
>
> Is there something I'm not seeing here?
>
>
> import java.util.*;
>
> public class Reduce {
>
>    static <T> T reduce(Iterable<? extends T> values, T initial,  
> {T,T=>T} reducer) {
>        T result = initial;
>        for (T value : values) {
>            result = reducer.invoke(result, value);
>        }
>        return result;
>    }
>
>    public static void main(String[] args) {
>
>        List<Integer> values = Arrays.asList(1, 2, 3, 4, 5);
>
>        Integer initial = 0;
>
>        Number num = reduce(values, initial, {Number n1, Number n2  
> => n1.intValue() > n2.intValue() ? n1 : n2});
>        Integer i1 = reduce(values, initial, {Integer i1, Integer i2  
> => i1 + i2});
>        Integer i2 = reduce(values, initial, {int i1, int i2 => i1 +  
> i2});
>    }
> }
>
>
> Reduce.java:21: <T>reduce(java.lang.Iterable<? extends T>,T,{T,T =>  
> T}) in Reduce cannot be applied to  
> (java.util.List<java.lang.Integer>,java.lang.Integer,{int,int => int})
>        Integer i2 = reduce(values, initial, {int i1, int i2 => i1 +  
> i2});
>                     ^
> 1 error
>
>
> Regards,
>
> Mark
>
>

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