c++ - 为什么这段代码在 Clang++ 中有效，但在 G++ 中无效？

Question

考虑以下代码:

struct Foo
{
    int x, y;

    Foo() = default;
    Foo(const Foo&) = delete;
    Foo& operator=(const Foo&) = delete;
};

int main()
{
    Foo f1 {1, 2};
    Foo f2 = {1, 2};
}

使用 clang++ 编译不会产生错误:

$ clang++ --version
Apple LLVM version 4.2 (clang-425.0.28) (based on LLVM 3.2svn)
Target: x86_64-apple-darwin12.4.0
Thread model: posix
$ clang++ -std=c++11 -stdlib=libc++ -pedantic t.cpp -o out
...builds and runs fine...

然而，compiling with g++ 4.8.1 through ideone gives errors :

prog.cpp: In function ‘int main()’:
prog.cpp:12:17: error: no matching function for call to ‘Foo::Foo(<brace-enclosed initializer list>)’
     Foo f1 {1, 2};
                 ^
prog.cpp:12:17: note: candidate is:
prog.cpp:5:5: note: Foo::Foo()
     Foo() = default;
     ^
prog.cpp:5:5: note:   candidate expects 0 arguments, 2 provided
prog.cpp:13:19: error: could not convert ‘{1, 2}’ from ‘<brace-enclosed initializer list>’ to ‘Foo’
     Foo f2 = {1, 2};
                   ^

如果我删除 Foo(const Foo&) = delete; 那么它 compiles fine在 g++4.8.1 中。

我的代码中是否存在一个编译器忽略但另一个编译器没有忽略的错误？

Answer 1

C++11 8.5.1 [dcl.init.aggr] p1 定义聚合类型:

An aggregate is an array or a class (Clause 9) with no user-provided constructors (12.1), no brace-or-equal-initializers for non-static data members (9.2), no private or protected non-static data members (Clause 11), no base classes (Clause 10), and no virtual functions (10.3).

user-provided 在 8.4.2 [dcl.fct.def.default] p4 中定义:

... A special member function is user-provided if it is user-declared and not explicitly defaulted or deleted on its first declaration.

Foo 有两个用户声明的构造函数，这两个构造函数在它们的第一个声明中都被显式默认或删除，因此 Foo 是一个聚合。

GCC 是错误的。

编辑:This is in fact GCC bug 52707 .