Stream.toArray()

[Gernot Neppert]

Hi, you might want to look at java.util.Arrays.copyOf to get an idea of how
to specify a bound for an array-typed parameter!
Applied to Stream, the method would look like this:

public <A> A[] toArray(Class<? extends A[]> clazz);

Remarks:

1) I'm not actually proposing the above version, I like the one with the
supplied *component type* better!


2) I really miss the following method in java.lang.Class:

/**
Returns a class representing the Object class of this class.
If this class already represents an Object-derived (non-primitive) type,
simply returns {@code this} instance.
Otherwise, returns the class literal of the corresponding Java wrapper type.
*/
public Class<?> getObjectClass();

3) Given the above method in java.lang.Class, I think that the proper way
of handling the case in 1) when a primitive type is passed as the component
type should be to return an array of the corresponding wrapper type.




2012/12/5 Remi Forax <forax at univ-mlv.fr>

> On 12/05/2012 04:44 PM, David M. Lloyd wrote:
>
>> Agreed on the array class - another reason is that otherwise folks might
>> expect this to work:
>>
>> int[] foo = stream.toArray(int[].class);
>>
>
> and they will never expect this to work ?
>     int[] foo = stream.toArray(int.class);
>
> I've used an array class because this is what you want an instance of an
> array class,
> so I've tried:
>     public <A extends Object[]> A asArray(Class<A> clazz);
> to reject toArray(int[])  but for a reason that I don't understand you can
> not use Object[] as bound.
>
> Rémi
>
>
>
>> On 12/05/2012 09:39 AM, Brian Goetz wrote:
>>
>>> Agree on the general form -- toArray(clazz) is definitely better than
>>> the current bad alternatives offered by Collection.
>>>
>>> I prefer that the argument be the component class, not the array class.
>>>   I think toArray(Foo.class) is far more natural to users than
>>> toArray(Foo[].class).
>>>
>>> On 12/5/2012 10:33 AM, Remi Forax wrote:
>>>
>>>> Restarting a thread that ends without clear winner.
>>>>
>>>> Currently, Stream.toArray() is specified as:
>>>>    Object[] toArray()
>>>>
>>>> which is not what users want, given the lack of reified generics and the
>>>> fact that it's usually hard for a user to predict the number of elements
>>>> of a Stream,
>>>> the best signature seems to be:
>>>>    <A> A[] toArray(Class<A> arrayClass)
>>>> with arrayClass.isArray() returning true and
>>>> arrayClass.getComponentType().**isPrimitive() returning false
>>>> (or if you prefer Object[].class.**isAssignableFrom(arrayClass)
>>>> returning
>>>> true)
>>>>
>>>> example of usage,
>>>>    Person[] coolPersons =
>>>> persons.stream().filter(**person#isCool()).toArray(**Person[].class);
>>>>
>>>> cheers,
>>>> Rémi
>>>>
>>>>
>>
>>
>