• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
Servant of the Lord

Best practice for identical non-const and const functions?

8 posts in this topic

Occasionally, I have a function that is non-const, and an 99% identical function that is const, like this:
[CODE]Blah &Class::GetSomething()
{
return something;
}


const Blah &Class::GetSomething() const
{
return something;
}
[/CODE]
[size=2](Note: My actual code, in this specific case, isn't just an accessor - it's looking through a vector to find the right element to return)[/size]

The end result is that I have a two functions with identical code, but only the function declaration is different. How can I safely use the definition of one to implement both of them?


Here's the code I'm currently wanting to use it on, but I've hit the same situation several times previously:
[code]Layer::Ptr &Floor::GetLayer(const LayerName &layerName)
{
for(auto &layer : this->Layers)
{
if(layer->Name == layerName)
return layer;
}

static Layer::Ptr dummy;
return dummy;
}[/code]
1

Share this post


Link to post
Share on other sites
I believe this is one of those rare circumstances where a const_cast was considered acceptable, and the const method calls the non-const method.
1

Share this post


Link to post
Share on other sites
In Effective C++, they recommended removing having the non-const version call the const version and remove it with a const_cast. This assumes it is not a virtual function.

If they are virtual, you are best with the duplication, or having both of them call a separate private method that does the actual work.
0

Share this post


Link to post
Share on other sites
If you don't like the const_cast approach, another way to tackle it is to create a private static template function that does the work. Have one template argument be a pointer to the class and another be the return type. Ex:
[code]
class Foo {
public:
Data * get_data(const std::string & name) {
return get_data_impl<Data *>(this, name);
}
const Data * get_data(const std::string & name) const {
return get_data_impl<const Data *>(this, name);
}
private:
template <typename R, typename T> static R get_data_impl(T * self, const std::string & name) {
for (auto & data : self->data_) {
if (data.name == name) return &data;
}
return nullptr;
}

std::vector<Data> data_;
};
[/code]
1

Share this post


Link to post
Share on other sites
I've heard of the const_cast method, but it seemed... hackish. If this is the recommended approach, then I'm happy to adopt it.

The proper usage would then be:
[code]Blah &Class::GetSomething()
{
return const_cast<Blah&>(this->GetSomething());
}
const Blah &Class::GetSomething() const
{
return something;
}[/code]

But wouldn't that send the non-const GetSomething() into an infinite loop, because it'd call itself recursively?

So I'd actually have to do:
[code]const Class *const_this = const_cast<const Class*>(this);
return const_cast<Blah&>(const_this->GetSomething());[/code]

Is that the correct usage?
0

Share this post


Link to post
Share on other sites
For that kind of non-trivial accessor functions, I would introduce a third non-const function to do the real accessing, then add constness in your const version accessor.

[CODE]
SomeType & getSomething() {
return doGetSomething()
}
const SomeType & getSomething() const {
return const_cast<MyClass *>(this)->doGetSomething()
}
private:
SomeType & doGetSomething() {
// do real work here
}
[/CODE]

This code is adding constness to return value rather than removing constness.
Removing constness may be dangerous from semantic view because it allows modification on const object. Adding constness is safe.
Though the const version of getSomething() removes const from "this", it's safe as long as doGetSomething() doesn't change the object.
0

Share this post


Link to post
Share on other sites
I've only ever used this idiom as follows:

[code]Blah &Class::GetSomething()
{
return something;
}
const Blah &Class::GetSomething() const
{
return const_cast<Class*>(this)->GetSomething();
}[/code]

With the single explicit cast. However the other approaches migh suit your taste better :)
1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0