On Thu, 2 Nov 2023 at 15:53, Edward Catmur via Std-Proposals
<std-proposals_at_[hidden]> wrote:
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> On Thu, 2 Nov 2023 at 07:53, Chris Gary via Std-Proposals <std-proposals_at_[hidden]> wrote:
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>>> .... Just because you *can* collapse some property of containers to a simple true/false, doesn't mean we should add a conversion to actually do that.
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>> Its concise if used in conjunction with the Elvis operator:
>> populateWith( oneVec ?: orAnother )
>> printLine( errMsg ?: g_successMsg ) // these could be string_view or string
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>>> The whole if ("") vs. if (""sv) is a complete red herring - those
>>> don't appear in any generic context, and in fact those don't appear
>>> anywhere.
>>> Nobody writes that. Nobody is confused by it.
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>> Seconding this.
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> I would dispute that; we use std::string_view() (i.e. std::string_view(nullptr, 0)) as a sentinel value, distinct from ""sv. Indeed, we would regard ""sv as truthy, since it is engaged in the sense that its data() is non-null. (The same holds for std::span, of course).

How does that dispute anything?

Do you write if (""sv) somewhere?

> If you really want contextual conversion to bool, wrap in a type that has that conversion. C++ is the land of zero-overhead, after all. And in generic code, use std::ranges::empty().

Which doesn't work for non-ranges like pointers and optionals. If
there's an actual generic way to check that something has a value in
it,
be it singular or plural, you can write a generic check, and handle
the singular/plural difference elsewhere, in slightly less generic
generic
code. ranges::empty() isn't that generic check. The point of
suggesting that containers could be bool-checked is that a contextual
conversion
to bool would be that generic check. We can certainly entertain having
something else instead, but contextual conversions to bool are
already idiomatic and common. We have them for iostreams, for example.
We just don't have them for containers, because containers
for some reason want to be different, and that then gets explained by
funny corner cases with literals that nobody uses.

This is also not a zero-overhead question. If you don't need that
check, don't use it. That causes no overhead for you. The ability to
do such
a check for a container has no space or time overhead for those who
don't use it, so it conforms to any zero-overhead principle perfectly
fine.