[swift-evolution] Proposal: Initialization should not be required in precondition(false) case.

[Алексей Демедецкий]

+1 for this switch behavior. Can we also treat switch? as one with did not require default checking?

> I have a suggestion.
> Suppose we think of 'switch' as being like a non-optional type. The compiler does its thing and tries to ensure that the switched expression will match something, and enforces a default if it cannot verify a matching state.
> Could we force the switch? i.e. suffix the 'switch' keyword with an exclamation mark, to say: the programmer insists that one of these cases will match; there's no need for a default case, but if nothing matches then crash.
> 
> For example:
> let x:Int
> switch! expression
> {
> case ... { x = 1 }
> case ... { x = 2 }
> // no default. the ! signifies that the app should crash if none of these cases matches the expression
> }
> 
> 
> 
> 
> On Fri, Feb 12, 2016 at 5:32 PM, Chris Lattner via swift-evolution<swift-evolution at swift.org(mailto:swift-evolution at swift.org)>wrote:
> > On Feb 12, 2016, at 9:27 AM, Amir Michail<a.michail at me.com(mailto:a.michail at me.com)>wrote:
> > >>>
> > >>>What’s wrong with having the compiler explicitly check for “false”?
> > >>
> > >>Weird special cases make the compiler less predictable.
> > >
> > >True, but not having them requires deeper knowledge of the standard libraries.
> > >
> > >In practice, just checking for “false” would solve this problem.
> > 
> > That is not what you’re actually proposing.You are proposing that the compiler encode special knowledge of the precondition *library function* into the compiler, and teach it about a single special case.We don’t like the compiler to have special cases like this for a large number of reasons, in particular, if we did this, someone would file a bug asking for *their* equivalent reimplementation of precondition to have the same magic blessed behavior.
> > 
> > This is a slippery slope that leads to a lot of complexity downstream, it is better to keep the compiler simple and predictable.Also, as other people have pointed out, this has already been solved for you: just use preconditionFailure.
> > 
> > -Chris
> > _______________________________________________
> > swift-evolution mailing list
> > swift-evolution at swift.org(mailto:swift-evolution at swift.org)
> > https://lists.swift.org/mailman/listinfo/swift-evolution
> 
> 
>