Bitten by the lambda parameter name

Jonathan Gibbons jonathan.gibbons at
Tue Jul 16 17:44:22 PDT 2013

On 07/16/2013 04:59 PM, Zhong Yu wrote:
> On Tue, Jul 16, 2013 at 6:48 PM, maurizio cimadamore
> <maurizio.cimadamore at> wrote:
>> On 17-Jul-13 12:37 AM, Zhong Yu wrote:
>>> I don't think people have problems to keep track of scope stacks and
>>> associate a name with its closest definition. Do we have testimonies
>>> of confusions from other languages that allow reusing local names in
>>> lambda parameters?
>> Speaking about Java, there is a scoping rule that drives me crazy, and it's
>> the one for the for-each loop; it should be legal to say:
>> Collection<String> s = ...
>> for (String s : s) {
> I don't know if you are being sarcastic or not, but `for(s : s)` does
> not make any sense to me... something that contains itself?

In "for (String s: s)" the presumption would be that the second s
would refer to the collection defined on the previous line, and not
the foreach variable itself, since (as you point out) that would not
make any sense.

> But here's an example that I think does make sense and shoulda compiled
>          String string = ...;
>          ...
>          List<String> strings = ...;
>          for(String string : strings)  // reuse "string"
>              ...
>> ...
>> }
>> This example features the same kind of disambiguation pattern that I've seen
>> applied in most examples here - stuff on the left of the ':' (or '->') has
>> one meaning, stuff on the right has another meaning.
>> The only example I would be more comfortable with, is the last one you sent,
>> where you use the same parameter name in two different nesting levels. This
>> is slightly different from what we have discussed so far.
>> Maurizio
>>> On Tue, Jul 16, 2013 at 6:25 PM, maurizio cimadamore
>>> <maurizio.cimadamore at> wrote:
>>>> On 16-Jul-13 11:59 PM, Remi Forax wrote:
>>>>> On 07/17/2013 12:40 AM, maurizio cimadamore wrote:
>>>>>> On 16-Jul-13 11:17 PM, Dan Smith wrote:
>>>>>>>>     StringBuilder builder = createText(StringBuilder.class, builder
>>>>>>> -> builder.append("name"));
>>>>>> What is this meant to replace exactly? It's a shorthand for:
>>>>>> StringBuilder builder = new StringBuilder();
>>>>>> builder.append("name");
>>>>>> ?
>>>>>> Maurizio
>>>>> Again, I'm not sure why this is interesting to know exactly what the
>>>>> code does,
>>>>> Anyway, the code of createText allows you to create a mutable object
>>>>> by reflection, to initialize it and when you get the result,
>>>>> you have the guarantee that you can never see the object half
>>>>> initialized.
>>>> I'm asking about the code, because I think that if we are forcing people
>>>> to write code like that there might be a problem other than the scope
>>>> issue.
>>>> Having two variables so close with the same name is confusing - no
>>>> matter how the language will pan out in the end. YOu seem to imply that
>>>> using the same name is justified by the fact that the two objects are
>>>> really the same - but I'm less sure that many people will be able to
>>>> read your code and immediately grasp as to why the two variables are
>>>> named in the same way. I think a good API should minimize occurrences of
>>>> that for the users sake.
>>>> Maurizio
>>>>> Rémi

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