enumerator duplicated value attribute

[Daniel Gutson]

Hi,

   sometimes is important to prevent duplication of enumerators in the enumerations. That's why some compilers such as clang has the -Wduplicate-enum.

However there are cases such as ranges within enums, where enumerators define a category and then are followed by the first element of the category, with the same value.

enum Ranges

{

    CategoryX = 100,

       X1 = CategoryX,

       X2,

       X3

     CategoryY = 200

       // ...

};

In order to allow such cases coexist with the useful diagnostic, I propose adding an enumerator attribute, such as [[allow_duplicate]]

enum Ranges

{

    CategoryX = 100 [[allow_duplicate]],

       X1 = CategoryX,

       X2,

       X3

     CategoryY = 200 [[allow_duplicate]]

       // ...

};

This way, we can have the diagnostic and also explicit the intention that in those cases it is OK to have a repeated value.

Comments?

    Daniel.

--

Who’s got the sweetest disposition?
One guess, that’s who?
Who’d never, ever start an argument?
Who never shows a bit of temperament?
Who's never wrong but always right?
Who'd never dream of starting a fight?
Who get stuck with all the bad luck?

[Chris Hallock]

On Friday, September 7, 2018 at 2:55:57 PM UTC-4, Daniel Gutson wrote:

Hi,

   sometimes is important to prevent duplication of enumerators in the enumerations. That's why some compilers such as clang has the -Wduplicate-enum.

However there are cases such as ranges within enums, where enumerators define a category and then are followed by the first element of the category, with the same value.

enum Ranges

{

    CategoryX = 100,

       X1 = CategoryX,

       X2,

       X3

     CategoryY = 200

       // ...

};

In order to allow such cases coexist with the useful diagnostic, I propose adding an enumerator attribute, such as [[allow_duplicate]]

enum Ranges

{

    CategoryX = 100 [[allow_duplicate]],

       X1 = CategoryX,

       X2,

       X3

     CategoryY = 200 [[allow_duplicate]]

       // ...

};

This way, we can have the diagnostic and also explicit the intention that in those cases it is OK to have a repeated value.

That warning triggers only on implicit duplicates, so you're all good.

[Arthur O'Dwyer]

On Friday, September 7, 2018 at 11:55:57 AM UTC-7, Daniel Gutson wrote:

Hi,

   sometimes is important to prevent duplication of enumerators in the enumerations. That's why some compilers such as clang has the -Wduplicate-enum.

However there are cases such as ranges within enums, where enumerators define a category and then are followed by the first element of the category, with the same value.

enum Ranges

{

    CategoryX = 100,

       X1 = CategoryX,

       X2,

       X3

     CategoryY = 200

       // ...

};

What Chris said: this code is already acceptable to Clang.

However, if you do ever run into a situation where Clang is giving you a warning that is "usually correct but I don't want to see it in this particular case," there already exists markup to indicate that situation:

enum Ranges {

    CategoryX = 100,

    X1 = CategoryX,

    X2,

    X3,

#pragma clang diagnostic push

#pragma clang diagnostic ignored "-Wduplicate-enum"

    DeprecatedNameX1 = X1,

    DeprecatedNameX2,

    DeprecatedNameX3,

#pragma clang diagnostic pop

};

Unfortunately, Clang currently has what-I-consider-a-bug in that it requires you to put the pragma on the first occurrence of the value, rather than on the duplicate occurrence. I've filed a bug report.

–Arthur

[gmis...@gmail.com]

I haven't ever had a need for this feature, but since clang supports a warning for it, it seems it might be reasonable to have it as a standard feature. Which is what the OP is asking for?

So it's good you provided the information that there is a solution that might work for his compiler, but would you vote for a standard way to do this? I think that's the question.