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Function parameter types not inferred in the presence of default arguments #11322

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lihaoyi opened this issue Dec 19, 2018 · 4 comments
Open

Function parameter types not inferred in the presence of default arguments #11322

lihaoyi opened this issue Dec 19, 2018 · 4 comments
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fixed in Scala 3 This issue does not exist in the Scala 3 compiler (https://github.com/lampepfl/dotty/) infer typer
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@lihaoyi
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lihaoyi commented Dec 19, 2018 •
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@ def foo(i: Int, j: Int) = i
defined function foo

@ foo(_, 1)
res5: Int => Int = ammonite.$sess.cmd5$$$Lambda$1703/0x0000000800a05040@396e6d9

@ def bar(i: Int, j: Int, k: Int = 2) = i
defined function bar

@ bar(_, 1)
cmd7.sc:1: missing parameter type for expanded function ((x$1: <error>) => bar(x$1, 1))
val res7 = bar(_, 1)
               ^
Compilation Failed

Seems like scala/scala#7340 missed a case; I would expect eta expansion to work for both
@SethTisue
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@adriaanm shall we milestone this for RC1, or not?

@adriaanm
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I don’t think I’ll be able to add support for named/defaults by the RC. let’s schedule for 2.13.1

@adriaanm adriaanm self-assigned this Jan 16, 2019
@adriaanm adriaanm added this to the 2.13.1 milestone Jan 16, 2019
@szeiger szeiger modified the milestones: 2.13.1, 2.13.2 Aug 28, 2019
@SethTisue SethTisue modified the milestones: 2.13.2, 2.13.3 Feb 6, 2020
@SethTisue SethTisue modified the milestones: 2.13.3, 2.13.4 May 12, 2020
@dwijnand dwijnand modified the milestones: 2.13.4, Backlog Oct 20, 2020
@SethTisue SethTisue added the fixed in Scala 3 This issue does not exist in the Scala 3 compiler (https://github.com/lampepfl/dotty/) label Oct 20, 2020
@dwijnand
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dwijnand commented Oct 20, 2020 •
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There's already the issue that you can't invoke def foo(x: Int = 1) with simply foo:

scala> def foo(x: Int = 1) = x.toString
def foo(x: Int): String

scala> foo
       ^
       error: missing argument list for method foo
       Unapplied methods are only converted to functions when a function type is expected.
       You can make this conversion explicit by writing `foo _` or `foo(_)` instead of `foo`.

@SethTisue
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SethTisue commented Oct 20, 2020 •
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There's already the issue that you can't invoke def foo(x: Int = 1) with simply foo:

that's as expected, I think, since Dotty aims to eliminate any need for foo _ syntax to exist, so just foo by itself eta-expands:

Starting dotty REPL...
scala> def foo(x: Int = 1) = x.toString                                                                                 
def foo(x: Int): String
def foo$default$1: Int

scala> foo                                                                                                              
val res0: Int => String = Lambda$1223/289710123@13ef7fa1

but it's kind of a tangent, since this ticket is about lambdas, not about eta-expansion per se. I will re-title the ticket not to refer to "eta expansion".

@SethTisue SethTisue changed the title Improved eta-expansion doesn't work for methods with default arguments Function parameter types not inferred in the presence of default arguments Oct 20, 2020
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