[cfe-dev] c++ question: can lambda be used in VLA?

[Richard Smith via cfe-dev]

Sure, yes, that's one way of allowing this, but why do you want to? What
would justify the added complexity of allowing this special case?

On Tue, May 24, 2016 at 2:47 PM, Akira Hatanaka via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> I believe this is not allowed in standard c++ but is allowed as a C99
> extension.
>
> I can silence the error if I replace the call to ParseConstantExpression
> at ParseDecl.cpp:6098 with ParseExpression, but it also causes other
> regression tests to fail.
>
> I also tried adding a flag IsArrayBound to
> ExpressionEvaluationContextRecord, which indicates the expression is used
> for an array bound. The value of the flag is checked In
> Sema::PopExpressionEvaluationContext and diagnostics for lambda expression
> are not emitted if the flag is true.
>
> On Wed, May 11, 2016 at 3:37 PM, Akira Hatanaka <ahatanak at gmail.com>
> wrote:
>
>> clang currently errors out if I use lambda to compute the size of an
>> array:
>>
>> $ cat t.cpp
>> int foo3();
>>
>> void foo() {
>>   unsigned char a1[([](int a) {return a; })(1)];
>> }
>>
>> $ clang++ t.cpp -c -std=c++11
>>
>>  *error: **a lambda expression may not appear inside of a constant
>> expression*
>>
>>   unsigned char a1[([](int a) { return a; })(1)];
>>
>>
>> I was wondering why this isn't allowed since clang supports VLA. If a1 is
>> a VLA, the size of the array doesn't have to be a constant expression, so
>> it seems that we should be able to use lambda in this example?
>>
>
>
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