Bitten by the lambda parameter name

maurizio cimadamore maurizio.cimadamore at
Tue Jul 16 16:48:47 PDT 2013

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) {

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.

> 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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