Re: C23 thoughts and opinions

Thiago Adams <thiago.adams@gmail.com> writes:

On 24/05/2024 16:45, Keith Thompson wrote:

Thiago Adams <thiago.adams@gmail.com> writes:

On 23/05/2024 18:49, Keith Thompson wrote:

error: 'constexpr' pointer initializer is not null
5 |     constexpr char * s[] = {"a", "b"};
>
>
Then we were asking why constexpr was used in that case.

Why not?

>
When I see a constexpr I ask if the compiler is able to compute
everything at compile time. If not immediately it is a bad usage in my
view.

I don't understand.  Do you object because it's not *immediately
obvious* that everthing can be computed at compile time?  If so, why
should it have to be?

>
My understanding is that constexpr is a tip for the compiler. Does not
ensure anything. Unless you use where constant expression is required.
So I don't like to see constexpr  where I know it is not a constant
expression.

Your understanding is incorrect.  "constexpr" is not a mere hint.

In C23, an object defined with "constexpr" must be initialized with a
constant expression.  C++ has similar rules.  Attempting to initialize
it with a non-constant expression requires a diagnostic.

    int non_const = 42;
    constexpr int bad = non_const; // invalid, must be diagnosed

I'd be surprised to see a C or C++ compiler that failed to diagnose such
an error.  Have you run into this, or are you speculating?

Given that the C++ code

    constexpr const char * s[] = {"a", "b"}; // I added "const"

compiles successfully, you can safely assume that the initializer can be
and is evaluated at compile time.

C++ has consteval
(https://en.cppreference.com/w/cpp/language/consteval) . When I first
saw it I thought it was a joke.

And I know just the newsgroup where it can be discussed.

[...]

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */