Thank you everyone for help, highly appreciated!
On Sunday, 28 June 2015 23:37:46 UTC+1, andrew cooke wrote:
>
> On Sunday, 28 June 2015 10:13:42 UTC-3, ks wrote:
>>
>> Hello Andrew,
>>
>> Thanks!
>>
>> the other answer is on the money, but, in this particular case, it seems
>>> to me that you might want to have a function that could take both of those,
>>> with the idea that you never get more than max_num_items, but that if you
>>> find max_iter_id before that, the sequence stops there.
>>>
>>> in that case, named args would be more suitable. something like
>>>
>>> function getitems(; max_num_items=-1, max_iter_id=...)
>>>
>>
>> In this case it would work nicely because all the cases make sense: none,
>> one (any), or both.
>>
>>
>>>
>>> where you might still have a special type for item id, but also have a
>>> special singleton that means "none" (like -1 means unlimited for
>>> max_num_items).
>>>
>>> then you could specify none (all items), either, or both.
>>>
>>
>> So you'd have a parent and two child types?:
>>
>> ItemId
>> / \
>> ExistingItemId NoneItemId (Singleton)
>>
>> What would be the difference of using one type ItemId and "nothing" to
>> denote "none"?:
>>
>> getitems(; max_num_items = -1, max_item_id = nothing )
>>
>> I also read about Nullable{T} type, perhaps it could be used as well in
>> this case.
>>
>
> any of those would work. you could also do something "dirtier" with a -ve
> sign if you were using a signed int for item IDs, but "real" IDs were
> positive.
>
> for example:
>
> immutable ItemId
> id::Int
> end
>
> then ItemId(-1) could be used to mean "no value".
>
> it depends how "serious" you want to be about making things type safe.
>
> andrew
>
>
>
>> Thanks again,
>> Krystian
>>
>>
>>>
>>> andrew
>>>
>>>
>>> On Friday, 26 June 2015 23:30:45 UTC-3, ks wrote:
>>>>
>>>> Hello everyone,
>>>>
>>>> I've just started to write a bit of code in Julia and I'm still
>>>> exploring the best ways of doing this and that. I'm having this small
>>>> problem now and wanted to ask for your advice.
>>>>
>>>> I'd like to have two methods that retrieve some items. The first method
>>>> takes the max number of items that should be retrieved. And the second
>>>> method takes the max item id.
>>>>
>>>> getitems( maxnumitems )
>>>> getitems( maxitemid )
>>>>
>>>> In both cases the argument has the same type: Int. So how do I take the
>>>> advantage of multiple dispatch mechanism in this situation? And is
>>>> multiple
>>>> dispatch really the recommended way of handling a situation like this one?
>>>> Here're some alternatives that I thought of:
>>>>
>>>> 1. Use different function names: getitems, getitems_maxid. Not too
>>>> elegant as you mix purpose and details of function usage in its name.
>>>> 2. Use named arguments. This will cause the function implementation to
>>>> grow (a series of if / else), again not too elegant.
>>>> 3. Define a new type: ItemId which behaves exactly as Int but can be
>>>> used to 'activate' multiple dispatch (one function would use Int and the
>>>> second one would use ItemId). Generally not the best approach if you have
>>>> methods each having an argument that should be really represented as an
>>>> Int
>>>> rather than a new type.
>>>> 4. ...?
>>>>
>>>> What would you recommend ?
>>>>
>>>> Thank you,
>>>> ks
>>>>
>>>
