CODEWITHSUNDEEP
c++macrostypedefc-preprocessordeprecated
azmeuk
azmeuk

Reputation: 4536

Deprecate old name for class in C++

I work on a framework that has massively renamed all its classes and functions, I created a transition header allowing to use old names:

#define OldClassA NewClassA
#define OldClassB NewClassB
...

Now I would like the compiler to warn the user when the old name is used. How can I do this?

int main(){
  NewClassA newA;
  OldClassA oldA; // <-- This one would emit a warning
}

Upvotes: 21

Views: 2850

Answers (4)

forkrul
forkrul

Reputation: 524

Since the release of C++14, you can now use the [[deprecated]] attribute, independent of the compiler (so long as the compiler fully supports C++14, of course).

In your case, you would use:

[[deprecated]]
typedef NewClassA OldClassA;

// You can also include a message that will show up in the compiler
// warning if the old name is used:

[[deprecated("OldClassA is deprecated; use NewClassA instead.")]]
typedef NewClassA OldClassA;

Note that this is only supported in gcc-4.9 (if using gcc) and you will need to specify -std=c++1y. I do not know about MSVC; clang supports this as of version 3.4.

See http://josephmansfield.uk/articles/marking-deprecated-c++14.html for more details on how to deprecate things other than just typedefs.

Upvotes: 7

Tony Delroy
Tony Delroy

Reputation: 106246

This is likely highly compiler specific.

For GCC, the reference page at http://gcc.gnu.org/onlinedocs/gcc-3.2/gcc/Type-Attributes.html describes the deprecated attribute and has examples for typedefs which I think should suit your needs:

typedef NewClassA OldClassA __attribute__ ((deprecated));

Clang has somethign similar, see http://clang.llvm.org/docs/LanguageExtensions.html

For Visual C++, you could try its deprecated declaraton/pragma: http://msdn.microsoft.com/en-us/library/044swk7y(v=vs.80).aspx

Upvotes: 8

Cassio Neri
Cassio Neri

Reputation: 20543

As said by others, this is very compiler specific. Assuming your classes are defined with the new name. Here is what you can do with GCC and MSVC:

class NewClassA {}; // Notice the use of the new name.

// Instead of a #define, use a typedef with a deprecated atribute:

// MSVC
typedef NewClassA __declspec(deprecated) OldClassA;

// GCC
//typedef NewClassA __attribute__((deprecated)) OldClassA;

int main(){
    NewClassA newA;
    OldClassA oldA;
}

MSVC yields:

warning C4996: 'OldClassA': was declared deprecated

GCC yields:

warning: 'OldClassA' is deprecated

No warning is emmited for NewClassA newA; by either compiler.

Upvotes: 25

user1744056
user1744056

Reputation:

Many compilers support #warning directive. E.g. VS: http://msdn.microsoft.com/en-us/library/aa266053(v=vs.60).aspx or GCC: http://gcc.gnu.org/onlinedocs/cpp/Diagnostics.html

#warning "old class name is used". Or in C++11 you can use static_assert.

Something like this:

#ifdef OldClassA
   #warning "old class name is used"

Upvotes: 1

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