Remove irrefutable match pattern

[changvvb]

Fixes #10614
Remove irrefutable match pattern, so that scala3 has the same behavior as scala2.

[liufengyun]

Thanks @changvvb 👍

Instead of removing the tests, can we adapt them?

[b-studios]

Great, thanks @changvvb ! Could you maybe also adjust the docs (Sources) accordingly.

[changvvb]

Thanks @changvvb 👍

Instead of removing the tests, can we adapt them?

I thought they are meaningless because almost all of these tests commented by // error are compiled successfully.
Deleting these tests is really too rough. I try to inspect them.

[liufengyun]

Thanks @changvvb 👍
Instead of removing the tests, can we adapt them?

I thought they are meaningless because almost all of these tests commented by // error are compiled successfully.
Deleting these tests is really too rough. I try to inspect them.

Fair enough. I thought Scala 2.13.4 issues a warning for the code below and we need to do the same as well:

scala > val Some(x) = Option(3)

But it does not.

[changvvb]

Fair enough. I thought Scala 2.13.4 issues a warning for the code below and we need to do the same as well:

scala > val Some(x) = Option(3)

But it does not.

I tried to compile val Some(x) = Option(3) both on scala 2.13.4 and scala 3, but no warning appeared.
On the other hand, they both show warning with Option(3) match { case Some(x) => x }

[liufengyun]

Fair enough. I thought Scala 2.13.4 issues a warning for the code below and we need to do the same as well:

scala > val Some(x) = Option(3)

But it does not.

I tried to compile val Some(x) = Option(3) both on scala 2.13.4 and scala 3, but no warning appeared.
On the other hand, they both show warning with Option(3) match { case Some(x) => x }

Yes, I got the same result. Then it's fine to remove them. Could you please rebase and update the docs, as suggested by @b-studios ?

[changvvb]

@b-studios @liufengyun
http://dotty.epfl.ch/docs/reference/changed-features/pattern-bindings.html introduce case for for expressions

This code gives a compile-time error in Scala 3.1 whereas in Scala 2 the list elems is filtered to retain only the elements of tuple type that match the pattern (x, y). The filtering functionality can be obtained in Scala 3 by prefixing the pattern with case:
for (case (x, y) <- elems) yield (y, x) // returns List((2, 1), (4, 3))

and

Generator ::= [‘case’] Pattern1 ‘<-’ Expr

Now, is it necessary to retain it?

[liufengyun]

@b-studios @liufengyun
http://dotty.epfl.ch/docs/reference/changed-features/pattern-bindings.html introduce case for for expressions

This code gives a compile-time error in Scala 3.1 whereas in Scala 2 the list elems is filtered to retain only the elements of tuple type that match the pattern (x, y). The filtering functionality can be obtained in Scala 3 by prefixing the pattern with case:
for (case (x, y) <- elems) yield (y, x) // returns List((2, 1), (4, 3))

and

Generator ::= [‘case’] Pattern1 ‘<-’ Expr

Now, is it necessary to retain it?

I think it's worthwhile to keep it and make sure it works.

[liufengyun]

@changvvb Thanks for your PR. We need to meet a deadline tomorrow, therefore I made a new PR #10793 .

[changvvb]

@changvvb Thanks for your PR. We need to meet a deadline tomorrow, therefore I made a new PR #10793 .

OK, I will close this PR.
I see they are different implements while #10793 drop Pattern2 [‘:’ Type | Ascription] ‘=’ Expr syntax but keep irrefutable match pattern in Scala 3.