Pointer ofNull method naming

[Ty Young]

On 11/13/19 6:01 PM, Maurizio Cimadamore wrote:
> Sorry, still not getting what you are trying to say. Let's pop back; 
> you have this function:
>
> int foo(Pointer<Pointer<Byte>> array, Pointer<Integer> size);
>
> Can you please explain what this function is expected to do? What are 
> the inputs and what are the outputs? How is 'size' connected 'array'? 


Pointer<Pointer<Byte>> arrayPointer = 
Bar.scope().allocate(NativeTypes.CHAR.pointer());

Pointer<Integer> sizePointer = Bar.scope().allocate(NativeTypes.INT);


Bar.foo(sizePointer, sizePointer);

Array<Byte> bytes = arrayPointer.get().withSize(size.get());

for(int i = 0; i < bytes.length(); i++)
     System.out.println(bytes.get(i));


Is how you're supposed to use it, but if you aren't interested in in the 
bitmask values you can just do:


arrayPointer.get().get()


which returns the first array element, saving both a Pointer and array 
allocation.



> What is that 'int' return value?


It's a "Bool" in C. Just returns whether the function call succeeded or not.


>
> I vaguely understand (from your previous emails) that the 'array' is 
> expected to have a certain encoding where first element is 'size' (of 
> what?) 


It's... complicated. The example provided is extremely simplified. The 
*actual* function uses 6 parameters, including enums(ints in Java) as 
well as index values to produce different results for a wide range of 
things. It's nuts.


What the byte value at index 0 represents depends on the arguments 
passed to this unholy abomination of a function, like the number of fans 
or displays connected. Some of the parameters are even optional.


> then you have some element bitmasks. But it's not clear whether the 
> 'array' is provided as input by the user, or is expected to be filled 
> by the function (same for 'size').


Both.


>
> Maurizio
>
> On 13/11/2019 23:01, Ty Young wrote:
>>
>> On 11/13/19 4:28 PM, Maurizio Cimadamore wrote:
>>>
>>> On 13/11/2019 22:15, Ty Young wrote:
>>>>
>>>> On 11/13/19 3:19 PM, Maurizio Cimadamore wrote:
>>>>>
>>>>> On 13/11/2019 12:43, Ty Young wrote:
>>>>>>
>>>>>> On 11/13/19 2:28 AM, Maurizio Cimadamore wrote:
>>>>>>> I'm ok with making the documentation more precise (I'm not sure 
>>>>>>> I like ofTyped()). Can you please clarify a bit what you mean by 
>>>>>>> 'filler' ? Like passing null ptr to a struct setter?
>>>>>>
>>>>>>
>>>>>> Not struct types but more primitive native types like 
>>>>>> Pointer<Byte> or Pointer<Integer>.
>>>>>>
>>>>>>
>>>>>> As an example, you have a function like this:
>>>>>>
>>>>>>
>>>>>> int foo(Pointer<Pointer<Byte>> array, Pointer<Integer> size);
>>>>>>
>>>>>>
>>>>>> But what you're actually interested in is at index 0 of the 
>>>>>> array, so "size" isn't needed and allocating a new Pointer would 
>>>>>> be a waste.
>>>>>
>>>>> Not sure I follow - if you are interested in index 0, doesn't that 
>>>>> mean that the array would need to have at least _one_ element 
>>>>> (e.g. size >= 1) ?
>>>>
>>>>
>>>> It does. It's just that the data that is actually desired is 
>>>> located at index 0, so doing:
>>>>
>>>>
>>>> array.get().get()
>>>>
>>>>
>>>> returns index 0 anyway.
>>>>
>>>>
>>>> For context, the function in question returns a Pointer to an array 
>>>> in the format:
>>>>
>>>>
>>>> Index 0 = number of items
>>>>
>>>> index 4 * number of item = bitmask of a given item
>>>
>>> Really confused by this example - if the size is always at position 
>>> 0 of the array, then what is the second argument Pointer<Integer> 
>>> used for?
>>
>>
>> "size" is the amount of something connected to the system, not the 
>> Pointer<Integer> size.
>>
>>
>> So the bitmask of item 1 is located at index 4, item 2 at 8, etc. in 
>> the array.
>>
>>
>>>
>>> I'm trying to understand whether this is really a 'new' use for 
>>> Pointer.ofNull, or whether you are just exploiting the fact that the 
>>> underlying function you are using happens to work even if the second 
>>> parameter is null. 
>>
>>
>> It does exploit the lack of null checks *technically* although you 
>> could just as easily lazily allocate a non null Pointer of the 
>> desired type to do the same thing. Would providing something like 
>> that be out of API scope?
>>
>>
>> Although, it's never explained(nor have I tried it) whether a Pointer 
>> allocated from a different scope can be used in another one so maybe 
>> that isn't even possible? If it is, then what's the point of Scope 
>> class anyway?
>>
>>
>>> in other words, I'm having problems understand what you mean by this 
>>> 'filler' capability of Pointer.ofNull.
>>
>>
>> The function requires a pointer be passed even if you aren't 
>> interested in what's inside that pointer after calling the function, 
>> therefor it's "filler".
>>
>>
>>>
>>> Maurizio
>>>
>>>>
>>>>
>>>> However, one might only be interested in index 0 or in this case, 
>>>> the number of items, so allocating another Pointer just to make the 
>>>> function call seems like a waste.
>>>>
>>>>
>>>> It seems like *some* functions check whether a given Pointer is 
>>>> null or not but not all do such as the functions I'm working with. 
>>>> It just fills the array Pointer regardless.
>>>>
>>>>
>>>>>
>>>>> Maurizio
>>>>>
>>>>>
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> (p.s. in these cases we have been also discussing bringing back 
>>>>>>> special treatment for Java null, so that null is re-interpreted 
>>>>>>> to Pointer.ofNull)
>>>>>>
>>>>>>
>>>>>> I haven't gone too deep down the rabbit hole, but I see 
>>>>>> "LayoutTypeImpl.nullType" in BoundedPointer. Isn't that the null 
>>>>>> interpretation for a Pointer?
>>>>>>
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> Maurizio
>>>>>>>