Bitten by the lambda parameter name

[Remi Forax]

On 07/15/2013 07:05 PM, Maurizio Cimadamore wrote:
> On 15/07/13 17:27, Remi Forax wrote:
>> On 07/15/2013 05:59 PM, Maurizio Cimadamore wrote:
>>> On 15/07/13 16:37, Remi Forax wrote:
>>>> On 07/15/2013 05:34 PM, Maurizio Cimadamore wrote:
>>>>> On 15/07/13 16:32, Maurizio Cimadamore wrote:
>>>>>> On 15/07/13 16:28, Remi Forax wrote:
>>>>>>> On 07/15/2013 05:13 PM, Maurizio Cimadamore wrote:
>>>>>>>> On 15/07/13 15:52, Remi Forax wrote:
>>>>>>>>> This snippet not compile,
>>>>>>>>>     Kind kind = ...
>>>>>>>>>     partySetMap.computeIfAbsent(kind, kind -> new 
>>>>>>>>> HashSet<>()).add(party);
>>>>>>>>>
>>>>>>>>> Each time I write more than a hundred lines of codes that use 
>>>>>>>>> some lambdas,
>>>>>>>>> I fall into this trap.
>>>>>>>>>
>>>>>>>>> It's very annoying !
>>>>>>>>>
>>>>>>>>> Rémi
>>>>>>>>>
>>>>>>>>>
>>>>>>>> Annoying yes - but there is a reason for it? If we provide 
>>>>>>>> special scoping for lambda parameters then we will never be 
>>>>>>>> able to add control abstraction syntax in a nice way; not 
>>>>>>>> saying that it's something we want - but it's good to have 
>>>>>>>> option open at least.
>>>>>>>
>>>>>>> It's a crystal ball argument, in the future if we do that then ...
>>>>>>> It usually doesn't work because between now and the future, the 
>>>>>>> way the feature will be introduced will change.
>>>>>>>
>>>>>> Well, yes and no - I remember we discussed a lot whether a lambda 
>>>>>> should look (semantically) more like a block or an inner class. 
>>>>>> We decided it should look like the former. This is a consequence 
>>>>>> of that decision. I think that mixing and matching semantics on a 
>>>>>> by-need basis is not a good idea.
>>>>> And - one might argue the code you are trying to write is not that 
>>>>> readable in the first place (adding random suffixes just to get it 
>>>>> through javac is not very elegant readability-wise, but it does 
>>>>> convery the concept that the two references of 'kind' which occur 
>>>>> very close one to the other are indeed unrelated).
>>>>>
>>>>> Maurizio
>>>>
>>>> Most of the time, there are not unrelated because the two variables 
>>>> carry the same reference like in Map.computeIfAbsent.
>>>> Correctly naming things (variables, methods, types, etc) is one of 
>>>> the hardest things you do when you write code,
>>>> in that context, having to find two different names for the same 
>>>> things is really weird.
>>>
>>> But - back to your code, couldn't the lambda be shared among all 
>>> uses of computeIfAbsent that target your partySetMap?
>>
>> I use computeIfAbsent because I want my Map to act as a cache, so 
>> there is only one call to computeIfAbsent.
> I still kinda think yours is more a problem of having to forcefully 
> put a name where something like '_' (i.e. in Scala) would have been 
> fine, rather than the fact that you are forced to pick a different name.

I often use 'unused' instead of the wunderbar in Java.
Anyway, sometime the key is useful and calling map.computeIfAbsent(key, 
key -> ...) is better than
map.computeIfAbsent(key, thisIsTheSameKeyButWithADifferentName -> ...).

Rémi

>
> Maurizio
>>
>>>
>>> Maurizio
>>
>> Rémi
>>
>>>>
>>>> Rémi
>>>>
>>>>>>
>>>>>> Maurizio
>>>>>>> In this peculiar case, if we add control abstraction syntax we 
>>>>>>> will use a different syntax,
>>>>>>> so it's very annoying for no reason.
>>>>>>>
>>>>>>>>
>>>>>>>> Maurizio
>>>>>>>
>>>>>>> Rémi
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>