default ctor for date types ? about date HOT 2 CLOSED

Thanks for the nice words.

My rationale to-date for not having them (for example for year_month_day) is:

• The default constructor would not be higher performance than the {y, m, d} constructor.
• It is difficult to choose a value for the default constructed object that is not surprising.
• It is easy to supply a "default value" of your own choosing for different situations.

For an example of the latter:

#include "date.h"
#include <iostream>
#include <fstream>

void
input(std::istream& is, date::year_month_day& x)
{
    int y, m, d;
    is >> y >> m >> d;
    // Don't modify x if the read failed
    if (!is.fail())
        x = date::year{y}/m/d;
}

int
main()
{
    std::ifstream infile("test.dat");
    while (infile)
    {
        using namespace date::literals;
        auto a_date = jan/0/0;  // initialize to !ok()
        input(infile, a_date);
        if (a_date.ok())
            std::cout << a_date << '\n';
        else
            break;
    }
}

In this example I want to "default" the date to something that is !ok(). If the de-serialization works, it should set it to something that is ok().

I have not yet come across a compelling use case where I really do need default constructors. And newing arrays of things is not compelling in modern C++ (use vector instead).

I am open to being shown compelling use cases for default constructors for these types: Use cases that demonstrate advantages that will outweigh the disadvantage of having a surprising default value no matter what gets chosen.

from date.

Thanks for the elaborate clarification.
Fair enough, I will try to make up some examples.

from date.