为什么Scala无法优化以下内容：
一个。
implicit def whatever[A](a: A) = new { ... }
为：
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类型？我希望Scala编译器能够执行这种优化，因为写入样式 b 太难看了（因为，1。逻辑的局部性丢失了，2。你必须不必要地为这些额外的显式类创建名称） ， a 的效果远远低于 b 。
答案 0 :(得分：3)
我认为可以，这可以通过编译器插件完成，看起来像
@extension implicit def whatever[A](a: A) = new { ... }
但我不知道是否有人写过这样的插件......
更新：
如果我编译这个文件：
object Main {
implicit def option[A](a: A) = new { def id = a }
def foo(x: String) = x.id
}
并反编译foo的代码，仍然涉及反射：
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
比较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
}
反编译：
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
}
答案 1 :(得分：2)
我也读过这个，并且经常想问同样的问题。但在2.8，我正在尝试：
object Main {
implicit def whatever[A](a: A) = new { def foo = "bar" }
}
当我javap它时：
public final class Main$$anon$1 extends java.lang.Object{
public java.lang.String foo();
public Main$$anon$1();
}
看起来好消息，不是吗？
更新您可以使用此trac item
跟踪此优化