On Sun, Mar 23, 2025 at 1:09 PM Sebastian Wittmeier via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> Again the same question as Thiago asked Muhammad:
>
> Is it only another name for *#pragma once*?
>
>
>
> There were reasons, why *#pragma once* has not been standardized so far.
>

There were three major categories of objections to it.

One, we do not standardize pragmas. Not even when major implementations
pretty much agree on the intent behind it, and what it's supposed to do
(from a user point of view).

Two, "#pragma once" is not well-specified in what it does, and in those
corner cases major implementations differ. They are the kinds of corner
cases that your build environment should prevent, but when they do happen,
different tools do something else.

Three, "#pragma once" is not well-specifyable in the C++ standard. The
standard does not refer to "files" anywhere other than in std::filesystem
(library), and has no good definition of "the same file". Adding that would
be a *lot* of additional wording, a lot of churn and a lot of meetings in
getting the words correct to mean what it should mean.

And in the end, what does that get us? The ability for people that use
"#pragma once" to keep using it? The ability to say "it's in the standard
now!"?

None of those are sufficient to explain the cost of making it happen. And
*that* is why it was voted down last time.

It'd be great if, when we have a new attempt at this, we propose something
that addresses *all* concerns that make it fail. Yes, this fixes #1, but at
best it's the 5th attempt to do so. It doesn't even start on 2 or 3, which
were the main reasons it was not voted in.