On 6/18/21 12:40 AM, Mathias LANG wrote:
On Thursday, 17 June 2021 at 21:41:28 UTC, Steven Schveighoffer wrote:
A final switch on an enum complains if you don't handle all the enum's
cases. I like this feature.
However, sometimes the data I'm switching on is coming from elsewhere
(i.e. a user), and while I want to enforce that the data is valid
(it's one of the enum values), I don't want to crash the program if
the incoming value is not correct. But final switch doesn't let me
declare a default case (to throw an exception instead).
If I use a non-final switch, then my code might forget to handle one
of the cases.
Oh, and to throw a monkey wrench in here, the value is a string, not
an integer. So I can't use std.conv.to to verify the enum is valid
(plus, then I'm running a switch twice).
Any ideas on better ways to handle this?
Well, if you receive an `enum` that have an out of bounds value, your
problem lies in the caller, not the callee. You're breaking the most
fundamental promise of a type, that is, the values it can take. And you
obviously also break any `@safe` function by feeding it this value.
Yeah, I know. But I'm not receiving an enum. I'm receiving a string. But
I want to handle a certain set of those strings everywhere. So what I
tried is to make an enum that has those strings. Then I would use final
switches whenever I handle it, so if I add a new string to the list, the
compiler will tell me where I missed handling that new one.
So instead of thinking in terms of `enum`, I would say, think in them of
the value, and generate the switch:
```D
SWITCH: switch (myRawValue)
{
static foreach (EV; NoDuplicates!(EnumMembers!MyEnum))
{
case EV:
// Handle;
break SWITCH;
}
default:
throw new Exception("Invalid value: " ~ myRawValue);
}
```
The // Handle then becomes a new switch. Though maybe I can group some
of them together.
I may as well use std.conv.to at that point.
I think that's what I'm probably going to do, I just wondered if there
was a better way.
-Steve
