Big problem with Small programs

[Sean Kelly]

Todor Totev wrote:
>> Walter Bright wrote:
>>>   Try using enums instead of const variables, they don't take up any 
>>> space in the object file.
>>
>> Thanks, but that makes only a dent in the overhead.
> 
> 
> Actually using enums instead of consts have a very nice side effect.
> Consider this declaration from win32:
> 
> HANDLE CreateFileW(LPCWSTR, DWORD, DWORD, LPSECURITY_ATTRIBUTES, DWORD, 
> DWORD, HANDLE);
> 
> Now, which invocation is correct?
> 
> CreateFile("a", OPEN_EXISTING, FILE_SHARE_READ, null, GENERIC_READ ...)
> or
> CreateFile("a", OPEN_EXISTING, GENERIC_READ, null, FILE_SHARE_READ ...)
> or even
> CreateFile("a", GENERIC_READ, OPEN_EXISTING, null, FILE_SHARE_READ ...)?
> 
> The compiler happily accepts all of them.
> 
> Using enums, we have:
> 
> enum FILE_SHARE {
>   READ  = 1,
>   WRITE = 2,
>   BOTH  = READ | WRITE
> }
> 
> enum DISPOSITION {
>   CREATE_ALWAYS = 1,
>   OPEN_EXISTING = 2
> }
> 
> void CreateFile(char[] fileName, DISPOSITION disposition, FILE_SHARE 
> share) {}
> 
> int main() {
>   // compiler allows unknown flags
>   CreateFile("filename", cast(DISPOSITION)4, FILE_SHARE.READ);
> 
>   // when we swap the arguments by mistake
>   CreateFile("filename", FILE_SHARE.READ, DISPOSITION.CREATE_ALWAYS);
> 
>   return 0;
> }
> 
> This way if I make an error the compiler will very helpfully tell me
> what exactly is happening. Consider: CreateFont has 14 parameters,
> if the IDE does not help me i'd make an error when I use it, trust me
> 
> On the other hand, when a new version of Windows come with expanded options
> I can just use the new numbers without breaking anything while the d 
> package is
> updated.
> 
> The dotnet framework uses enums and I really like the idea.

I agree that this is a great feature of D.  And if you're willing to 
adapt the Win32 headers to use this convention then I would gladly 
accept them :-)


Sean