He-Pin commented on PR #983:
URL: https://github.com/apache/incubator-pekko/pull/983#issuecomment-1901809838
```scala
object Cast {
val NotApplied: Any => Any = _ => NotApplied
def cast[A](a: Any): A = a.asInstanceOf[A]
def castWithMatch[A](a: Any): A = a match {
case NotApplied => ???
case a: A @unchecked => a
}
def castWithRef[A](a: Any): A = {
if (a.asInstanceOf[AnyRef] eq NotApplied) {
???
} else {
a.asInstanceOf[A]
}
}
}
```
and the bytecode:
```scala
// class version 52.0 (52)
// access flags 0x31
public final class org/apache/pekko/stream/impl/Cast$ {
// compiled from: Cast.scala
ATTRIBUTE Scala : unknown
ATTRIBUTE ScalaInlineInfo : unknown
// access flags 0x19
public final static INNERCLASS java/lang/invoke/MethodHandles$Lookup
java/lang/invoke/MethodHandles Lookup
// access flags 0x19
public final static Lorg/apache/pekko/stream/impl/Cast$; MODULE$
// access flags 0x1A
// signature Lscala/Function1<Ljava/lang/Object;Ljava/lang/Object;>;
// declaration: NotApplied extends scala.Function1<java.lang.Object,
java.lang.Object>
private final static Lscala/Function1; NotApplied
// access flags 0x9
public static <clinit>()V
L0
LINENUMBER 25 L0
NEW org/apache/pekko/stream/impl/Cast$
DUP
INVOKESPECIAL org/apache/pekko/stream/impl/Cast$.<init> ()V
PUTSTATIC org/apache/pekko/stream/impl/Cast$.MODULE$ :
Lorg/apache/pekko/stream/impl/Cast$;
L1
LINENUMBER 27 L1
INVOKEDYNAMIC apply()Lscala/Function1; [
// handle kind 0x6 : INVOKESTATIC
java/lang/invoke/LambdaMetafactory.altMetafactory(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
// arguments:
(Ljava/lang/Object;)Ljava/lang/Object;,
// handle kind 0x6 : INVOKESTATIC
org/apache/pekko/stream/impl/Cast$.$anonfun$NotApplied$1(Ljava/lang/Object;)Lscala/Function1;,
(Ljava/lang/Object;)Lscala/Function1;,
5,
1,
(Ljava/lang/Object;)Lscala/Function1;
]
PUTSTATIC org/apache/pekko/stream/impl/Cast$.NotApplied :
Lscala/Function1;
L2
LINENUMBER 25 L2
RETURN
MAXSTACK = 2
MAXLOCALS = 0
// access flags 0x1
// signature ()Lscala/Function1<Ljava/lang/Object;Ljava/lang/Object;>;
// declaration: scala.Function1<java.lang.Object, java.lang.Object>
NotApplied()
public NotApplied()Lscala/Function1;
L0
LINENUMBER 27 L0
GETSTATIC org/apache/pekko/stream/impl/Cast$.NotApplied :
Lscala/Function1;
ARETURN
L1
LOCALVARIABLE this Lorg/apache/pekko/stream/impl/Cast$; L0 L1 0
MAXSTACK = 1
MAXLOCALS = 1
// access flags 0x1
// signature <A:Ljava/lang/Object;>(Ljava/lang/Object;)TA;
// declaration: A cast<A>(java.lang.Object)
public cast(Ljava/lang/Object;)Ljava/lang/Object;
// parameter final a
L0
LINENUMBER 28 L0
ALOAD 1
ARETURN
L1
LOCALVARIABLE this Lorg/apache/pekko/stream/impl/Cast$; L0 L1 0
LOCALVARIABLE a Ljava/lang/Object; L0 L1 1
MAXSTACK = 1
MAXLOCALS = 2
// access flags 0x1
// signature <A:Ljava/lang/Object;>(Ljava/lang/Object;)TA;
// declaration: A castWithMatch<A>(java.lang.Object)
public castWithMatch(Ljava/lang/Object;)Ljava/lang/Object;
// parameter final a
L0
LINENUMBER 31 L0
ALOAD 0
INVOKEVIRTUAL org/apache/pekko/stream/impl/Cast$.NotApplied
()Lscala/Function1;
DUP
IFNONNULL L1
POP
ALOAD 1
IFNULL L2
GOTO L3
L1
FRAME SAME1 scala/Function1
ALOAD 1
INVOKEVIRTUAL java/lang/Object.equals (Ljava/lang/Object;)Z
IFEQ L3
L2
FRAME SAME
GETSTATIC scala/Predef$.MODULE$ : Lscala/Predef$;
INVOKEVIRTUAL scala/Predef$.$qmark$qmark$qmark ()Lscala/runtime/Nothing$;
ATHROW
L3
LINENUMBER 32 L3
FRAME SAME
ALOAD 1
INSTANCEOF java/lang/Object
IFEQ L4
ALOAD 1
ARETURN
L4
LINENUMBER 30 L4
FRAME SAME
NEW scala/MatchError
DUP
ALOAD 1
INVOKESPECIAL scala/MatchError.<init> (Ljava/lang/Object;)V
ATHROW
L5
LOCALVARIABLE this Lorg/apache/pekko/stream/impl/Cast$; L0 L5 0
LOCALVARIABLE a Ljava/lang/Object; L0 L5 1
MAXSTACK = 3
MAXLOCALS = 2
// access flags 0x1
// signature <A:Ljava/lang/Object;>(Ljava/lang/Object;)TA;
// declaration: A castWithRef<A>(java.lang.Object)
public castWithRef(Ljava/lang/Object;)Ljava/lang/Object;
// parameter final a
L0
LINENUMBER 36 L0
ALOAD 0
INVOKEVIRTUAL org/apache/pekko/stream/impl/Cast$.NotApplied
()Lscala/Function1;
ASTORE 2
L1
LINENUMBER 37 L1
ALOAD 1
ALOAD 2
IF_ACMPNE L2
L3
LINENUMBER 38 L3
GETSTATIC scala/Predef$.MODULE$ : Lscala/Predef$;
INVOKEVIRTUAL scala/Predef$.$qmark$qmark$qmark ()Lscala/runtime/Nothing$;
ATHROW
L2
LINENUMBER 40 L2
FRAME APPEND [scala/Function1]
ALOAD 1
ARETURN
L4
LOCALVARIABLE sentinel Lscala/Function1; L1 L4 2
LOCALVARIABLE this Lorg/apache/pekko/stream/impl/Cast$; L0 L4 0
LOCALVARIABLE a Ljava/lang/Object; L0 L4 1
MAXSTACK = 2
MAXLOCALS = 3
// access flags 0x1019
public final static synthetic
$anonfun$NotApplied$1(Ljava/lang/Object;)Lscala/Function1;
// parameter final x$1
L0
LINENUMBER 27 L0
GETSTATIC org/apache/pekko/stream/impl/Cast$.MODULE$ :
Lorg/apache/pekko/stream/impl/Cast$;
INVOKEVIRTUAL org/apache/pekko/stream/impl/Cast$.NotApplied
()Lscala/Function1;
ARETURN
L1
LOCALVARIABLE x$1 Ljava/lang/Object; L0 L1 0
MAXSTACK = 1
MAXLOCALS = 1
// access flags 0x2
private <init>()V
L0
LINENUMBER 25 L0
ALOAD 0
INVOKESPECIAL java/lang/Object.<init> ()V
RETURN
L1
LOCALVARIABLE this Lorg/apache/pekko/stream/impl/Cast$; L0 L1 0
MAXSTACK = 1
MAXLOCALS = 1
// access flags 0x100A
private static synthetic
$deserializeLambda$(Ljava/lang/invoke/SerializedLambda;)Ljava/lang/Object;
ALOAD 0
INVOKEDYNAMIC
lambdaDeserialize(Ljava/lang/invoke/SerializedLambda;)Ljava/lang/Object; [
// handle kind 0x6 : INVOKESTATIC
scala/runtime/LambdaDeserialize.bootstrap(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;[Ljava/lang/invoke/MethodHandle;)Ljava/lang/invoke/CallSite;
// arguments:
// handle kind 0x6 : INVOKESTATIC
org/apache/pekko/stream/impl/Cast$.$anonfun$NotApplied$1(Ljava/lang/Object;)Lscala/Function1;
]
ARETURN
MAXSTACK = 1
MAXLOCALS = 1
}
```
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