Proposal: Named parameters for Java APIs

Language Design
1

val st = new StringTokenizer(str = s, delim = x, returnDelims = true)

vs:

val st = new StringTokenizer(s, x, true)

The former is more readable but does not compile.

Note: I think Java 8 can emit param names now (with the -parameter option) so we can atleast support this for the JDK libs, local Java sources and any other external Java library compiled with the -paramter option: https://docs.oracle.com/javase/tutorial/reflect/member/methodparameterreflection.html

4 Likes
2
1 Like
3

Yes, in scala/scala#4735 Simon already implemented emitting them. I agree the logical next step is to also read them from javac-produced classfiles and let you specify them.

4

We have that already :blush:

> cat A.java
public class A {
  public static int flup(int fancy) { return fancy + 1; }
}
> javac -parameters A.java
> scala -version
Scala code runner version 2.12.2 -- Copyright 2002-2017, LAMP/EPFL and Lightbend, Inc.
> scala -e 'println(A.flup(fancy = 33))'
34
>
1 Like
6

Iā€™m not sure what you mean - it should work for all java libraries that were compiled with -parameters. Unfortunately the Java standard library is not compiled with that flag, as far as I can tell

> unzip -d . -j /Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/rt.jar java/lang/String.class

> javap -v -classpath . String | grep MethodParameters -C 2
Warning: Binary file String contains java.lang.String
>

> javap -v -classpath . A | grep MethodParameters -C 2
   #8 = Utf8               flup
   #9 = Utf8               (I)I
  #10 = Utf8               MethodParameters
  #11 = Utf8               fancy
  #12 = Utf8               SourceFile
--
--
      LineNumberTable:
        line 2: 0
    MethodParameters:
      Name                           Flags
      fancy
>