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Limited backporting of Java 8 libraries #22

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bisher3 opened this issue Jun 20, 2014 · 8 comments
Closed

Limited backporting of Java 8 libraries #22

bisher3 opened this issue Jun 20, 2014 · 8 comments

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@bisher3
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bisher3 commented Jun 20, 2014

What would it take to support some of Java 8's libraries such as Stream, Collector, Collectors?
@luontola
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First would be needed a separately available library that has exactly the same APIs. The only difference would be that they would probably have to be in a different package, because IIRC the JVM has security features to prevent adding user classes in the java.* namespace. It would be relatively simple to rename the references in bytecode to use other classes. The maven-shade-plugin might even be able to do it already now, or at least with small modifications.

(I can't think of a way to fully backport all the stuff that was added as default methods to Iterable, Collection etc. because default methods are polymorphic.)

@luontola
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Or then just use a third-party library that does the same thing. Googling for java functional library finds multiple alternatives.

@naixx
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naixx commented Jun 20, 2014

Guava works with retrolambda really well and has similar api

@mperry
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mperry commented Jun 20, 2014

FunctionalJava is awesome for functional programming in Java (I contribute to the project). The 4.0 release supports Java 8 and 4.1 supports both Java 7 and 8. We use retrolambda to backport lambdas to do this. To be backwards compatible we moved all the concrete or default methods of the interface to static methods in another class.

Of course, this is still painful compared to more expressive languages.

@bisher3
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bisher3 commented Jun 20, 2014

Thanks everyone, great insight. So how feasible would it be to "bridge" parts of Java 8 libs with third party libs while using retrolambda? I know it would probably be better to just use something like FunctionalJava, but for developers that have just started learning functional style using Java 8 and would like to apply it to their immediate projects ( such as Android development ) focusing on one set of libs would be desirable.

@luontola
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I don't want to include it in Retrolambda - it would increase the scope of this project too much, and anyways it can be implemented as a separate project.

Also I don't see a good use case for compiling the code against java.util.* classes and then running it against a different set of third party classes. Why not just directly compile it against those third party classes? The only difference from development point of view is that the imports are different (or else the automatic conversion would anyways not be possible).

Learning a new library takes only an hour or two. That amount of time is easily wasted in debugging bugs due to minor differences between the original classes and their replacements, because it would be very hard to make the library backport 100% compatible.

@bisher3
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bisher3 commented Jun 22, 2014

Well yes when you put it that way I have to agree.

@bisher3 bisher3 closed this as completed Jun 22, 2014
@jodastephen
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Just noting for anyone doing a backport that java.time (JSR-310) is available as ThreeTen-Backport on Java SE 6 and 7.

Arneball added a commit to Arneball/retrolambda that referenced this issue Aug 11, 2014
@Arneball
package testpackage;
8e13c80 
public interface MyInterface {
    default String def() {
        return "[" + toString() + ", " + "def]";
    }

    default String join(MyInterface other) {
        return def() + other.def();
    }
}

class C implements MyInterface{}  compiles to:

public class testpackage.MyClass implements testpackage.MyInterface {
  public testpackage.MyClass();
    Code:
       0: aload_0
       1: invokespecial luontola#16                 // Method java/lang/Object."<init>":()V
       4: return

  public java.lang.String join(testpackage.MyInterface);
    Code:
       0: aload_0
       1: aload_1
       2: invokestatic  luontola#46                 // Method testpackage/MyInterfacehelper.join:(Ltestpackage/MyInterface;Ltestpackage/MyInterface;)Ljava/lang/String;
       5: areturn

  public java.lang.String def();
    Code:
       0: aload_0
       1: invokestatic  luontola#49                 // Method testpackage/MyInterfacehelper.def:(Ltestpackage/MyInterface;)Ljava/lang/String;
       4: areturn
}

Where testpackage.MyInterfacehelper is compiled to
public class testpackage.MyInterfacehelper {
  private testpackage.MyInterfacehelper();
    Code:
       0: aload_0
       1: invokespecial luontola#9                  // Method java/lang/Object."<init>":()V
       4: return

  public static java.lang.String def(testpackage.MyInterface);
    Code:
       0: new           luontola#13                 // class java/lang/StringBuilder
       3: dup
       4: invokespecial luontola#14                 // Method java/lang/StringBuilder."<init>":()V
       7: ldc           luontola#16                 // String [
       9: invokevirtual luontola#20                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      12: aload_0
      13: invokevirtual luontola#24                 // Method java/lang/Object.toString:()Ljava/lang/String;
      16: invokevirtual luontola#20                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      19: ldc           luontola#26                 // String ,
      21: invokevirtual luontola#20                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      24: ldc           luontola#28                 // String def]
      26: invokevirtual luontola#20                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      29: invokevirtual luontola#29                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      32: areturn

  public static java.lang.String join(testpackage.MyInterface, testpackage.MyInterface);
    Code:
       0: new           luontola#13                 // class java/lang/StringBuilder
       3: dup
       4: invokespecial luontola#14                 // Method java/lang/StringBuilder."<init>":()V
       7: aload_0
       8: invokeinterface luontola#35,  1           // InterfaceMethod testpackage/MyInterface.def:()Ljava/lang/String;
      13: invokevirtual luontola#20                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      16: aload_1
      17: invokeinterface luontola#35,  1           // InterfaceMethod testpackage/MyInterface.def:()Ljava/lang/String;
      22: invokevirtual luontola#20                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      25: invokevirtual luontola#29                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      28: areturn
}

==============
interface StaticTest {
    static <T> T staticMethod(T t) {
        return t;
    }
}
compiles to
public class testpackage.StaticTesthelper {
  private testpackage.StaticTesthelper();
    Code:
       0: aload_0
       1: invokespecial luontola#9                  // Method java/lang/Object."<init>":()V
       4: return

  public static <T> T staticMethod$static(T);
    Code:
       0: aload_0
       1: areturn
}

========

Brigde methods are generated properly in example:
public interface BridgeParent<T> {
    T get();
}
public interface StringBridges extends BridgeParent<String> {
    @OverRide
    default String get() {
        return "default method";
    }

    default String concrete() {
        return "concrete";
    }
}
public class testpackage.StringBridgeshelper
  SourceFile: "testpackage/StringBridges.java"
  minor version: 0
  major version: 50
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   luontola#1 = Utf8               testpackage/StringBridgeshelper
   luontola#2 = Class              luontola#1             //  testpackage/StringBridgeshelper
   luontola#3 = Utf8               java/lang/Object
   luontola#4 = Class              luontola#3             //  java/lang/Object
   luontola#5 = Utf8               testpackage/StringBridges.java
   luontola#6 = Utf8               <init>
   luontola#7 = Utf8               ()V
   luontola#8 = NameAndType        luontola#6:luontola#7          //  "<init>":()V
   luontola#9 = Methodref          luontola#4.luontola#8          //  java/lang/Object."<init>":()V
  luontola#10 = Utf8               get
  luontola#11 = Utf8               (Ltestpackage/StringBridges;)Ljava/lang/String;
  luontola#12 = Utf8               default method
  luontola#13 = String             luontola#12            //  default method
  luontola#14 = Utf8               concrete
  luontola#15 = String             luontola#14            //  concrete
  luontola#16 = Utf8               (Ltestpackage/StringBridges;)Ljava/lang/Object;
  luontola#17 = Utf8               testpackage/StringBridges
  luontola#18 = Class              luontola#17            //  testpackage/StringBridges
  luontola#19 = Utf8               ()Ljava/lang/String;
  luontola#20 = NameAndType        luontola#10:luontola#19        //  get:()Ljava/lang/String;
  luontola#21 = InterfaceMethodref luontola#18.luontola#20        //  testpackage/StringBridges.get:()Ljava/lang/String;
  luontola#22 = Utf8               Code
  luontola#23 = Utf8               LineNumberTable
  luontola#24 = Utf8               SourceFile
{
  private testpackage.StringBridgeshelper();
    descriptor: ()V
    flags: ACC_PRIVATE
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial luontola#9                  // Method java/lang/Object."<init>":()V
         4: return

  public static java.lang.String get(testpackage.StringBridges);
    descriptor: (Ltestpackage/StringBridges;)Ljava/lang/String;
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=1, locals=1, args_size=1
         0: ldc           luontola#13                 // String default method
         2: areturn
      LineNumberTable:
        line 9: 0

  public static java.lang.String concrete(testpackage.StringBridges);
    descriptor: (Ltestpackage/StringBridges;)Ljava/lang/String;
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=1, locals=1, args_size=1
         0: ldc           luontola#15                 // String concrete
         2: areturn
      LineNumberTable:
        line 13: 0

  public static java.lang.Object get(testpackage.StringBridges);
    descriptor: (Ltestpackage/StringBridges;)Ljava/lang/Object;
    flags: ACC_PUBLIC, ACC_STATIC, ACC_BRIDGE, ACC_SYNTHETIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokeinterface luontola#21,  1           // InterfaceMethod testpackage/StringBridges.get:()Ljava/lang/String;
         6: areturn
      LineNumberTable:
        line 6: 0
}
@Arneball Arneball mentioned this issue Aug 11, 2014
Closed
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5 participants
@luontola @jodastephen @mperry @naixx @bisher3