[PATCH] D28467: [Sema] Add warning for unused lambda captures

[Aaron Ballman via cfe-commits]

On Thu, Jan 19, 2017 at 4:37 AM, Malcolm Parsons
<malcolm.parsons at gmail.com> wrote:
> On 19 January 2017 at 03:47, Aaron Ballman <aaron.ballman at gmail.com> wrote:
>> It is not used in an unevaluated context -- that is a bug.
>
> It is an evaluated expression, but is it odr-used?
>
> C++14 [basic.def.odr] p3:
>
> A variable x whose name appears as a potentially-evaluated expression
> ex is odr-used by ex unless applying the lvalue-to-rvalue conversion
> (4.1) to x yields a constant expression (5.20) that does not invoke
> any nontrivial functions and, if x is an object, ex is an element of
> the set of potential results of an expression e, where either the
> lvalue-to-rvalue conversion (4.1) is applied to e, or e is a
> discarded-value expression (Clause 5). ...
>
> 5.20 [expr.const] p3:
>
> An integral constant expression is an expression of integral or
> unscoped enumeration type, implicitly converted to a prvalue, where
> the converted expression is a core constant expression. [ Note: Such
> expressions may be used as array bounds (8.3.4, 5.3.4), as bit-field
> lengths (9.6), as enumerator initializers if the underlying type is
> not fixed (7.2), and as alignments (7.6.2). — end note ]
>
> I read that as kDelta is not odr-used.
>
> GCC and ICC don't require kDelta to be captured either.

You are correct, it is not an odr use. MSVC is wrong to require the capture.

~Aaron

>
> --
> Malcolm Parsons