Re: Enable string_view assertions

[Jonathan Wakely <jwakely dot gcc at gmail dot com>]

On 14 March 2018 at 23:27, Jonathan Wakely wrote:
> Here's one way to generalize this idea. We could potentially replace
> most of the lightweight __glibcxx_assert checks with this, to get
> zero-overhead static checking at compile-time whenever possible (even
> in constexpr functions) and have optional run-time assertions for the
> remaining cases.

Thinking about this some more, we probably don't want to do this for
most __glibcxx_assert uses, because it's probably rare that we can
statically detect most errors in something like
std::vector::operator[]. I doubt we would catch many bugs that way, as
most bugs would involve non-constant indices and vectors that have
changed size dynamically at run-time.

It *might* be useful  in vector::front, vector::back, string::front,
deque::front etc. to catch bugs where users do:

std::string s;
// ...
someFunction(&s.front(), s.size());

It seems most valuable in constexpr functions (where we definitely
expect constant arguments in many cases) and where run-time arguments
will typically be constants, like in the attached patch for atomic
objects.

Attachment: patch.txt
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