Re: Falling through on switch-cases

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"Jon Skeet [C# MVP]" <skeet@xxxxxxxxx> wrote in message news:MPG.224b45d96c3561ebb8e@xxxxxxxxxxxxxxxxxxxxxxx
Ben Voigt [C++ MVP] <rbv@xxxxxxxxxxxxx> wrote:
Jon Skeet [C# MVP] wrote:
> Rudy Velthuis <newsgroups@xxxxxxxxxxxx> wrote:
>> Jon Skeet [C# MVP] wrote:
>>
>>> Ranges are a possibility, so long as you can always check that a
>>> value falls in only one range.
>>
>> The compiler should simply generate a compile error if the ranges
>> overlap, like it does in Pascal. Then, only one range can apply. If
>> you'd allow overlapping ranges, the first match could win.
>
> Yes - as I say, it's easy enough to tell for the built-in numeric
> types. There may be other types where it's not so obvious though.

switch is only allowed on built in integral types and string anyway

Well yes, at the moment - but if we're considering possible changes, we
should consider the possibility of a more flexible switch.

It really goes back to what the point of switch is. If it's to use a
lookup to avoid a series of if/else statements for performance reasons,
I'm not sure its place is really deserved in C#.

If its purpose is to find one matching piece of code from a number of
options, there are ways it could be significantly more flexible.

--
Jon Skeet - <skeet@xxxxxxxxx>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
World class .NET training in the UK: http://iterativetraining.co.uk


As a newbie/amateur, I was disappointed with both case statements and enums in C#; both are weaker than what I expected. (Almost everything else was way better than I expected!).

As I understand it, I have to write

..
..
..
thisday = (int) dayofweek.Sunday
..
..
..

switch (thisday);
{case (int) dayofweek.Sunday: dostuff();break;
case (int) dayofweek.Monday: dostuff(); break;
..
..}


What I was hoping for was:

thisday=Sunday;

switch (thisday);
{case Sunday: dostuff(); break;
case Monday: dostuff(); break;}

Or even:

switch(thisday);
{case Sunday: dostuff(); break;
case Monday..Friday: dostuff(); break;
case Saturday: dostuff(); break;}

The continual need to cast back to integers reduces the readability of the code.

Also, as someone else pointed out, the ++ operator for enums should loop. If you have a statement:

thisday++;

and thisday was (int)dayofweek.Saturday, it returns what in reality is an out-of-range enum (as there is no day of the week after Saturday).

What I think would have been more useful is thisday++ being equivalent to

thisday++; if (thisday>(int)dayofweek.Saturday) thisday=(int) dayofweek.Sunday;

or even better

thisday++; if (thisday>Saturday) thisday=Sunday;

Its probably too late to change this and keep backwards compatibility, so I think C# is stuck with ++ working for enums as it does for integers.

As somebody else pointed out, Pascal (now 30 years old) had user defined types which work a little like enums, but in a more readable, maintainable and intuitive form.

.

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