Fix #9829: Allow as in place of @ for pattern bindings

[odersky]

For 3.0: Can use either @ or as.
For 3.1: @ is deprecated.

[som-snytt]

"At-less shrugged."

[AdamPaynter]

I rather like this change. as definitely carries more explanatory value than @. My only tiny stumbling block is where the as keyword appears. Wouldn't it make more sense to say Pattern(...) as myVar instead of myVar as Pattern(...)? Don't get me wrong, if I could happily accept an arbitrary @, I can more than happily accept the as presented here. I was just curious if you could help me understand the choice.

[som-snytt]

@AdamPaynter the issue suggests https://dotty.epfl.ch/docs/reference/contextual/givens.html as a model for the order. I had the same reservation, given usages in other domains. But if I say, "I took you for a bounder," then it's the alias taken as a bounder, the underlying type. Similarly for any definition where the lhs introduces the binding and the rhs the definition.

[odersky]

I think it can go both ways. ML uses <pattern> as <var>. By contrast Visual Basic uses <var> As <type> as a binder (where we would use :).

[liufengyun]

LGTM

[liufengyun]

We need to update the syntax.md file with the syntax change.

[nafg]

Perhaps, if you believe in punctuated equilibrium

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On Thu, Sep 24, 2020, 7:35 AM som-snytt ***@***.***> wrote: Worth observing that this change encapsulates in miniature all that is laudable in the Dotty effort: a judicious willingness to continue to evolve, when others might have rested. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#9837 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAYAUAM6ZLLJZFRIPKEAW3SHMVGVANCNFSM4RTXYOMA> .