为什么不能优化隐式转换的这种情况？

Question

为什么Scala不能优化以下内容：

a。

implicit def whatever[A](a: A) = new { ... } 

到：

湾

class some$generated$name(a: A) { 
    ... 
} 
implicit def whatever[A](a: A) = new some$generated$name(a) 

？

为什么在这种情况下必须使用结构打字？我想Scala编译器执行此优化，在写作风格b是太丑陋（因为，1，逻辑的地方丢失，2.你必须不必要的发明名称为这些额外的明确的类），并一个性能远低于b。

Answer 1

我认为这可能，而这可以通过编译器插件来完成，看起来像

@extension implicit def whatever[A](a: A) = new { ... } 

但我不知道是否有人写然而，这样一个插件...

UPDATE：

如果我编译该文件：

object Main { 
    implicit def option[A](a: A) = new { def id = a } 

    def foo(x: String) = x.id 
} 

和反编译代码，反思仍在参与：

F:\MyProgramming\raw>javap -c Main$ 
Compiled from "Main.scala" 
public final class Main$ extends java.lang.Object implements scala.ScalaObject{ 
public static final Main$ MODULE$; 

public static {}; 
    Code: 
    0: new  #9; //class Main$ 
    3: invokespecial #12; //Method "<init>":()V 
    6: return 

public static java.lang.reflect.Method reflMethod$Method1(java.lang.Class); 
    Code: 
    0: getstatic  #20; //Field reflPoly$Cache1:Ljava/lang/ref/SoftReference; 
    3: invokevirtual #27; //Method java/lang/ref/SoftReference.get:()Ljava/lang/Object; 
    6: checkcast  #29; //class scala/runtime/MethodCache 
    9: ifnonnull  29 
    12: new  #23; //class java/lang/ref/SoftReference 
    15: dup 
    16: new  #31; //class scala/runtime/EmptyMethodCache 
    19: dup 
    20: invokespecial #32; //Method scala/runtime/EmptyMethodCache."<init>":()V 
    23: invokespecial #35; //Method java/lang/ref/SoftReference."<init>":(Ljava/lang/Object;)V 
    26: putstatic  #20; //Field reflPoly$Cache1:Ljava/lang/ref/SoftReference; 
    29: getstatic  #20; //Field reflPoly$Cache1:Ljava/lang/ref/SoftReference; 
    32: invokevirtual #27; //Method java/lang/ref/SoftReference.get:()Ljava/lang/Object; 
    35: checkcast  #29; //class scala/runtime/MethodCache 
    38: aload_0 
    39: invokevirtual #38; //Method scala/runtime/MethodCache.find:(Ljava/lang/Class;)Ljava/lang/r 
eflect/Method; 
    42: astore_1 
    43: aload_1 
    44: ifnull 49 
    47: aload_1 
    48: areturn 
    49: aload_0 
    50: ldc  #40; //String id 
    52: getstatic  #42; //Field reflParams$Cache1:[Ljava/lang/Class; 
    55: invokevirtual #48; //Method java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class 
;)Ljava/lang/reflect/Method; 
    58: astore_1 
    59: new  #23; //class java/lang/ref/SoftReference 
    62: dup 
    63: getstatic  #20; //Field reflPoly$Cache1:Ljava/lang/ref/SoftReference; 
    66: invokevirtual #27; //Method java/lang/ref/SoftReference.get:()Ljava/lang/Object; 
    69: checkcast  #29; //class scala/runtime/MethodCache 
    72: aload_0 
    73: aload_1 
    74: invokevirtual #52; //Method scala/runtime/MethodCache.add:(Ljava/lang/Class;Ljava/lang/ref 
lect/Method;)Lscala/runtime/MethodCache; 
    77: invokespecial #35; //Method java/lang/ref/SoftReference."<init>":(Ljava/lang/Object;)V 
    80: putstatic  #20; //Field reflPoly$Cache1:Ljava/lang/ref/SoftReference; 
    83: aload_1 
    84: areturn 

public java.lang.Object option(java.lang.Object); 
    Code: 
    0: new  #59; //class Main$$anon$1 
    3: dup 
    4: aload_1 
    5: invokespecial #60; //Method Main$$anon$1."<init>":(Ljava/lang/Object;)V 
    8: areturn 

public java.lang.String foo(java.lang.String); 
    Code: 
    0: aload_0 
    1: aload_1 
    2: invokevirtual #69; //Method option:(Ljava/lang/Object;)Ljava/lang/Object; 
    5: astore_2 
    6: aconst_null 
    7: astore_3 
    8: aload_2 
    9: invokevirtual #75; //Method java/lang/Object.getClass:()Ljava/lang/Class; 
    12: invokestatic #77; //Method reflMethod$Method1:(Ljava/lang/Class;)Ljava/lang/reflect/Metho 
d; 
    15: aload_2 
    16: iconst_0 
    17: anewarray  #71; //class java/lang/Object 
    20: invokevirtual #83; //Method java/lang/reflect/Method.invoke:(Ljava/lang/Object;[Ljava/lang 
/Object;)Ljava/lang/Object; 
    23: astore_3 
    24: aload_3 
    25: checkcast  #85; //class java/lang/String 
    28: checkcast  #85; //class java/lang/String 
    31: areturn 
    32: astore 4 
    34: aload 4 
    36: invokevirtual #91; //Method java/lang/reflect/InvocationTargetException.getCause:()Ljava/l 
ang/Throwable; 
    39: athrow 
    Exception table: 
    from to target type 
    8 24 32 Class java/lang/reflect/InvocationTargetException 


} 

与

object Main2 { 
    class Whatever[A](a: A) { def id = a } 

    implicit def option[A](a: A) = new Whatever(a) 

    def foo(x: String) = x.id 
} 

和反编译比较：

F:\MyProgramming\raw>javap -c Main2$ 
Compiled from "Main2.scala" 
public final class Main2$ extends java.lang.Object implements scala.ScalaObject{ 
public static final Main2$ MODULE$; 

public static {}; 
    Code: 
    0: new  #9; //class Main2$ 
    3: invokespecial #12; //Method "<init>":()V 
    6: return 

public Main2$Whatever option(java.lang.Object); 
    Code: 
    0: new  #16; //class Main2$Whatever 
    3: dup 
    4: aload_1 
    5: invokespecial #20; //Method Main2$Whatever."<init>":(Ljava/lang/Object;)V 
    8: areturn 

public java.lang.String foo(java.lang.String); 
    Code: 
    0: aload_0 
    1: aload_1 
    2: invokevirtual #30; //Method option:(Ljava/lang/Object;)LMain2$Whatever; 
    5: invokevirtual #34; //Method Main2$Whatever.id:()Ljava/lang/Object; 
    8: checkcast  #36; //class java/lang/String 
    11: areturn 

} 

F:\MyProgramming\raw>javap -c Main2$Whatever 
Compiled from "Main2.scala" 
public class Main2$Whatever extends java.lang.Object implements scala.ScalaObject{ 
public java.lang.Object id(); 
    Code: 
    0: aload_0 
    1: getfield  #14; //Field a:Ljava/lang/Object; 
    4: areturn 

public Main2$Whatever(java.lang.Object); 
    Code: 
    0: aload_0 
    1: aload_1 
    2: putfield  #14; //Field a:Ljava/lang/Object; 
    5: aload_0 
    6: invokespecial #22; //Method java/lang/Object."<init>":()V 
    9: return 

} 

Answer 2

我读到过了，经常要问同样的问题。但在2.8，我想出来：

object Main { 
    implicit def whatever[A](a: A) = new { def foo = "bar" } 
} 

当我的javap它：

public final class Main$$anon$1 extends java.lang.Object{ 
    public java.lang.String foo(); 
    public Main$$anon$1(); 
} 

看起来是个好消息，不是吗？

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