[Links] Known incompatibilities with scalac

[DarkDimius]

This issue is a list of issues where dotty by-design or by-intention does not support some of the code-patterns that were previously (partially) supported by scalac. Some of those features may be partially supported under -language:Scala2.

Dependent method types:

• disallowed dependent implicit methods Disallow dependent implicit methods. #1467

Overloading:

• disallowed overloading of parameter-less methods Fix #1457: Three incompatbilities with scalac #1465

Widening and constraint solving:

• vals infer less precise types than equivalent objects
• implicit search on with type parameters in contravariant positions works differently

Supercalls:

• restriction on super-calls inside traits: Default methods, mixin and invokeSpecial on JVM  #1392 (comment)

Early initialisers and DelayedInit:

• not supported Rewriting tool should warn on extending DelayedInit #559

Definitions:

• unnamed type parameters not supported: Class and method type parameters named _ no longer supported #235

Structural types:

• we haven't yet decided if we support them and how much would be supported def in structural type is rejected, but val is accepted #1175. This issue is linked with HList & record types.

Weak subtyping:

• not supported. Though constant widening is supported.

[smarter]

I think it would make more sense to collect these in a wiki page.

[DarkDimius]

I would have agreed if people were reading wikis. My sample suggest that only a very small percentage of people does.

[smarter]

That suggests that we should advertise it better :). But I think a wiki page among 20 wiki pages is going to be read more than one issue among 160 issues.

[smarter]

Also, just as a sample point, the github statistics indicate that the "Getting Started" page of the wiki is read by slightly more unique visitors (100 vs 93) than the main "Issues" page: https://github.com/lampepfl/dotty/graphs/traffic

[DarkDimius]

#1787

[liufengyun]

Major changes are now documented in http://dotty.epfl.ch/docs/index.html REFERENCE > OTHER CHANGED FEATURES & DROPPED FEATURES.

Minor changes/incompatibilities now temporarily locate in wiki: https://github.com/lampepfl/dotty/wiki/Known-incompatibilities-with-scalac