Error with C++11 uniform initialization of an array of type with explicit default constructor

[llvmbot]

Bugzilla Link	27052
Version	3.7
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor

Extended Description

I am getting an error when compiling the following snippet:

    struct Explicit {
        explicit Explicit() {}
    };

    struct A {
        A(): _a{} {}

        Explicit _a[5];
    };

    int main() {}

Clang 3.7.1 complains that error: chosen constructor is explicit in copy-initialization, both GCC 5.3 and MSVC 2015 compile fine. The behavior differs when I make the following changes:

• If I remove the explicit keyword, it compiles fine (of course).
• If I make the _a member a non-array, it compiles fine.
• If I change _a{} to the C++03-style _a(), it compiles fine.
• If I change _a{} to _a{Explicit{}, Explicit{}, Explicit{}, Explicit{}, Explicit{}}, it compiles fine.
• If I change the constructor to explicit Explicit() = default;, it compiles fine.

The problem is not just when using constructor initializer lists, but also when initializing the array as a variable like this:

    Explicit b[5]{};

This behavior seems rather arbitrary to me and since the "old" C++03-style works okay, I think it should have the same behavior in C++11.

This probably affects also older versions, didn't have a chance to test.

[AaronBallman]

Closing as Clang's behavior is correct and is consistent with other C++ compilers: https://godbolt.org/z/ejMPdfshe

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (llvmbot)

Details

| | | | --- | --- | | Bugzilla Link | [27052](https://llvm.org/bz27052) | | Version | 3.7 | | OS | Linux | | Reporter | LLVM Bugzilla Contributor | | CC | @DougGregor |

Extended Description

I am getting an error when compiling the following snippet:

    struct Explicit {
        explicit Explicit() {}
    };

    struct A {
        A(): _a{} {}

        Explicit _a[5];
    };

    int main() {}

Clang 3.7.1 complains that error: chosen constructor is explicit in copy-initialization, both GCC 5.3 and MSVC 2015 compile fine. The behavior differs when I make the following changes:

• If I remove the explicit keyword, it compiles fine (of course).
• If I make the _a member a non-array, it compiles fine.
• If I change _a{} to the C++03-style _a(), it compiles fine.
• If I change _a{} to _a{Explicit{}, Explicit{}, Explicit{}, Explicit{}, Explicit{}}, it compiles fine.
• If I change the constructor to explicit Explicit() = default;, it compiles fine.

The problem is not just when using constructor initializer lists, but also when initializing the array as a variable like this:

    Explicit b[5]{};

This behavior seems rather arbitrary to me and since the "old" C++03-style works okay, I think it should have the same behavior in C++11.

This probably affects also older versions, didn't have a chance to test.