Cannot use consteval functions inside initializer list on MSVC

Question

Consider that minimized code snippet:

#include <vector>

class Bar
{
public:
    constexpr Bar() {}
};

consteval Bar foo()
{
    return Bar();
}

int main()
{
    std::vector<Bar> bars{ foo(), foo() };
}

This doesn't compile on latest MSVC compiler (Visual Studio 2022 version 17.3.3), but does on Clang or GCC.

Compiler Explorer

Is the code somewhere ill formed, or it is a bug in MSVC?

I think (but I'm not positive) that since you are using an STL container (vector) to store a custom type (Bar), the problem is that no copy (or move) ctor is defined (the call `foo()` returns an rvalue). — Ronald Souza, Sep 12 '22 at 11:05
@RonaldSouza Possibly, but I doubt, since my original failing code was not using a STL container, and original `Bar` class was copyable. — prapin, Sep 12 '22 at 11:08
@RonaldSouza - Those operations are implicitly defined. There is nothing here to supress their generation. — StoryTeller - Unslander Monica, Sep 12 '22 at 11:08
Duplicate? [Different behavior of consteval in GCC and MSVC (not work)](https://stackoverflow.com/q/65396085/10871073) — Adrian Mole, Sep 12 '22 at 11:09
I'm 99% certain it's a gap in MSVC's implementation. Not near a PC to verify comfortably, though... — StoryTeller - Unslander Monica, Sep 12 '22 at 11:09
... the answer to the suggested dupe has a link to an MSDN blog that claims the issue is fixed, though. Seems to be incorrect. — Adrian Mole, Sep 12 '22 at 11:10
@StoryTeller-UnslanderMonica (and prapin): I see. Good point. — Ronald Souza, Sep 12 '22 at 11:11
@AdrianMole Maybe the same original bug source, but it seems that current MSVC compiles the snippets in linked question, so not completely a duplicate. — prapin, Sep 12 '22 at 11:14

score 9 · Accepted Answer · answered Sep 12 '22 at 13:06

9

From the comments, it looks like this is indeed a bug in MSVC.

Therefore I filled in a bug report on Visual Studio Community.

https://developercommunity.visualstudio.com/t/Cannot-use-consteval-functions-returning/10145209

answered Sep 12 '22 at 13:06

prapin

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In my Visual Studio 2022, gave compile error `error C7595: 'foo': call to immediate function is not a constant expression` – daparic Sep 12 '22 at 15:33

Cannot use consteval functions inside initializer list on MSVC

1 Answers1