Use #define macro in C++ to choose implementations from different namespaces

Question

The multiplatform engine we're developing for our game uses the EASTL to replace the STL, because of memory, performance and portability reasons. The EASTL can be found here:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2271.html

Because Visual Studio is really good for debugging the STL we're not using the EASTL on Windows while the engine is in development. Also some STL containers as std::queue, std::deque, ... aren't available in the EASTL. Because it doesn't matter we're using the eastl::string on Windows as well, because it's fine for debugging.

What we're doing until now is

#if (GIN_USE_EASTL)
    #define ginstl eastl
#else
    #define ginstl std
#endif

and GIN_USE_EASTL is defined as 0 on windows. The engine is called Ginkgo, thats where the GIN comes from.
We're using lists, vectors, ... like this

ginstl::list myList;
ginstl::vector myVector;

which works quite fine. But when we use a string or a queue, because of reasons I explained above, we have to write

eastl::string myString;
std::queue myQueue;

which is the reason why i'm posting here, because this is not optimal! What I want to do is use the ginstl:: macro for everything in the engine, without thinking about what implementation to use. So my approach on the problem was this:

#if (GIN_USE_EASTL)
    #define ginstl::list eastl::list
    #define ginstl::vector eastl::vector
    #define ginstl::string eastl::string
    #define ginstl::queue std::queue
#else
    #define ginstl::list std::list
    #define ginstl::vector std::vector
    #define ginstl::string eastl::string
    #define ginstl::queue std::queue
#endif

But unfortunalty that's not working, because the :: is not allowed in the #define macro. Is there any way to achieve the same thing (be able to specify which implementation I want to use for a specific datastructure) somehow different? I could go for

#define ginstl_list eastl::list

but I would prefer the structure from above! Is there a way (except writing a custom pre-processor) around the problem?

Do you actually **need** the EASTL (yet)? Why not use the default STL implementation until you know that it's actually insufficient for your needs? Premature optimization and all that :) — jalf, Jan 06 '12 at 19:02
actually no, we don't need it ATM, but for not using it now, the benefit of using ginstl:: would even be bigger, because we can just swap the implementation at the end. — v01pe, Jan 06 '12 at 19:08
And I forgot, we actually do use some eastl specific implementations of the string class (.toUpper(), .toLower(), ...) — v01pe, Jan 06 '12 at 20:04

score 6 · Answer 1 · answered Jan 06 '12 at 18:35

6

What about using namespace:

namespace ginstl
{
#if (GIN_USE_EASTL)
    using eastl::list
    using eastl::vector
    using eastl::string
    using std::queue
#else
    using std::list
    using std::vector
    using eastl::string
    using std::queue
#endif
}

answered Jan 06 '12 at 18:35

Mark B

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that sounds promising! will try it tomorrow (beer-o-clock)! – v01pe Jan 06 '12 at 19:37
Thanks for the helping lead! Could also have done it this way, but @Krizz's way is the more comfortable one, because using a different implementation then the default one if rare. And you also see at a glace where the exceptions are! – v01pe Jan 07 '12 at 00:34

score 5 · Accepted Answer · answered Jan 06 '12 at 18:43

5

Developing further on the Mark B's way (no need to list all types used):

namespace ginstl
{
#if (GIN_USE_EASTL)
    using namespace eastl;
#else
    using namespace std;
#endif
    using eastl::string
    using std::queue
}

answered Jan 06 '12 at 18:43

Krizz

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Awesome! Exactly what I needed, couldn't wait to try it, and it works! Just make sure to use it in a C++ environment (won't compile in C context) – v01pe Jan 07 '12 at 00:31
Of course, there is no such a thing as namespace in C. Glad to hear that it helped you. – Krizz Jan 07 '12 at 10:22

Ferruccio · Answer 3 · 2012-01-06T18:57:35.850

3

If you use namespace aliases instead of macros:

#if (GIN_USE_EASTL)
    namespace ginstl = eastl;
#else
    namespace ginstl = std;
#endif

You can then do this:

using namespace ginstl;
using std::queue;
using std::deque;

list<int> x; // from eastl or std, depending on GIN_USE_EASTL
queue<int> y; // always from std

edited Jan 06 '12 at 18:57

answered Jan 06 '12 at 18:50

Ferruccio

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I don't want to use the using lines in every file I'm using one of the structures, but thanks for the equals syntax… didn't know that existed – v01pe Jan 06 '12 at 20:01

Use #define macro in C++ to choose implementations from different namespaces

3 Answers3