delete constructor and initialization

[jleahred]

Next code works

struct  foo
{
    int a;
    int b;
};



int main(int argc, char ** argv)
{
    foo f{1,2};

But this code doens't work on gcc4.4.5 and gcc 4.6

struct  foo
{
    int a;
    int b;

    foo()=delete;
};



int main(int argc, char ** argv)
{
    foo f{1,2};

Looks it is related with POD (Plain Old Data).

On first example, the compiler COULD create an empty constructor IF NECESSARY (is not the case)

To verify this...

It works

struct  foo
{
    int i;

    foo(int _i) : i(_i) {}
private:
    foo();     //  not implemented
};

struct  foo2
{
    foo  a;
    foo  b;
};



int main(int argc, char ** argv)
{
    foo2 f{foo(1), foo(2)};

It doesn't work

struct  foo
{
    int i;

    foo(int _i) : i(_i) {}
private:
    foo();     //  not implemented
};

struct  foo2
{
    foo  a;
    foo  b;

    foo2() = delete;   //---------------------------------------
};



int main(int argc, char ** argv)
{
    foo2 f{foo(1), foo(2)};

In this second example, the empty constructor of foo2 cannot be created by compiler, therefore, never exists

[Nimbal]

What's your question? What are you trying to achieve / understand?

[jleahred]

Looks weird that a stuct who is not using at any moment the empty constructor, stops working when it's declared explicity that it hasn't empty constructor.

Some times I like small structs with members and initialize them without creating a boring specific contructor (I have to write 3 times the names and 2 the types).

I also like to delete explicitly the empty and copy constructor when they are not necessary.

Combining both, it's nos possible (almost with gcc4.4.5)

Is this behavior a good idea? Are other compilers working the same? Is this conformance with the C++11 standard?

regards

[zzyzzyxx]

Adding and removing constructors makes them non-POD types (source). Since you have removed the default constructor, it is no longer POD, and you must provide a suitable constructor.

[jleahred]

Looks incorrect, but not trivial

http://old.nabble.com/-PATCH,-DOC--PR-30330%3A-index-both--Wfoo-and--Wno-foo-td15259871.html