[dmd-beta] Migration path for enum Endian?

Jonathan M Davis jmdavisProg at gmx.com
Tue Sep 6 15:16:53 PDT 2011

On Tuesday, September 06, 2011 17:01:28 Andrei Alexandrescu wrote:
> On 9/6/11 4:52 PM, Jonathan M Davis wrote:
> > On Tuesday, September 06, 2011 17:03:30 Nick Sabalausky wrote:
> >> The names inside std.system.Endian were changed from UpperCamelCase to
> >> lowerCamelCase, which makes sense, but maybe the old names should
> >> still
> >> exist for migration?
> > 
> > Yu can't rename enum values without breaking code. Any final switches
> > would be broken if you left in the old values as would anything using
> > std.traits.EnumMembers.
> I think EnumMembers is used rarely enough to not warrant much worry. If
> final switch fails to compile because it doesn't handle all aliases of
> the same value, that's a bug in the compiler. So I think keeping old
> values alongside new ones is good practice.

I don't know how rare EnumMembers usage is, but it's definitely used. I use it 
in unit tests and the like. It's probably not a big issue for 
std.system.Endian though. Regardless, it was discussed in the pull request. I 
said that I hadn't provided duplicate enum values with the old names, and you 
merged it in that way.

> > A simple renaming is caught and pointed out quite well
> > by the compiler's spellchecker.
> Code breakage is what it is.

True. But this is easy-to-fix code breakage. My point is that you _can't_ avoid 
code breakage when renaming enums. It's just a question of what code you're 
going to break, how easy such breakage is going to fix, and how common it is. 
Renamings are going to be more common but very easy to fix. Something like 
EnumMembers may be less common, but it's going to be more subtle when it 
breaks, and the code which uses it would have to be changed to explicitly 
ignore duplicate enum values, which could be problematic.

- Jonathan M Davis

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