Utility functions in a namespace or in a class?

Question

Until now if I needed some commonly used utility functions I moved them into a utility class. In a way like this:

#pragma once

class QDate;
class QDateEdit;
class QDialog;
class QWidget;

class GuiUtils final
{
public:
    static void moveDialog( QDialog* aDialog, const int aMargin = 4 );
    static void setMainWidget( QWidget* aParent, QWidget* aChild, const int aMargin = 0 );

    static void setValueBlocked( QDateEdit* aDateEdit, const QDate& aDate );

private:
    GuiUtils();
};

class DateUtils final
{
public:
    static QDate today();
    static QDate yesterday();
    static QDate firstDayOfWeek();
    static QDate firstDayOfMonth();
    static QDate firstDayOfQuarter();
    static QDate firstDayOfYear();

    static int quarter( const QDate& aDate );
    static int quarter( const int aMonth );

private:
    DateUtils();
};

But I know that there is an other option for this. I could move all my functions into a namespaces. In a way like this:

#pragma once

class QDate;
class QDateEdit;
class QDialog;
class QWidget;

namespace gui_utils
{
    void moveDialog( QDialog* aDialog, const int aMargin = 4 );
    void setMainWidget( QWidget* aParent, QWidget* aChild, const int aMargin = 0 );

    void setValueBlocked( QDateEdit* aDateEdit, const QDate& aDate );
};

namespace date_utils
{
    QDate today();
    QDate yesterday();
    QDate firstDayOfWeek();
    QDate firstDayOfMonth();
    QDate firstDayOfQuarter();
    QDate firstDayOfYear();

    int quarter( const QDate& aDate );
    int quarter( const int aMonth );
};

For me it seems a better solution for creating a utility class than a namespace. I see that I need to type more, but if I need to define a new namespace for all utility function group it would look a bit extreme for me. I don't usually create new namespaces but classes every time so that's why I use the first option.

But now I would like to know that:

• is there any advantage of using a namespace for this purpose ?
• does it have a better performane of using namespaces for this purpose ?
• does it better fits in the concepts of C++ ?
• is there any other reason for using namespaces for this ?

I would like to know your opinions but I need explanations as well. I don't want to rewrite my existing codes and writing the new ones with a different style "just because". I need some language/performance based or any other kind of explanation why to use it in one or in another way.

Thanks for help.

Answer 1

I believe that in your case, using a namespace is a better choice for a variety of reasons.

For example:

1. It appears that your functions do not share data.
2. Namespaces enable ADL (Argument Dependent name Lookup).

See any of several style guides. Here is a clip from Google's:

*Nonmember, Static Member, and Global Functions Prefer placing nonmember functions in a namespace;... Rather than creating classes only to group static member functions which do not share static data, use namespaces instead. *