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kotlin - 在 Kotlin 中访问函数的默认参数值

转载 作者:行者123 更新时间:2023-12-01 01:49:18 25 4
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可以从函数扩展或其他任何地方访问函数的默认参数值吗?

fun DieRoll.cheatRoll():Int = roll(min = max -1)

fun roll(min: Int = 1, max: Int = 6): Int = (min..max).rand()

最佳答案

不,这是不可能的。默认值不可访问。它们只是包含在 bridge-method 中在字节码中:

fun test(a: Int = 123) {
}

fun test2() {
test()
test(100)
}

字节码中的结果:
public final test(int arg0) { //(I)V
<localVar:index=0 , name=this , desc=Lorg/guenhter/springboot/kt/Fun;, sig=null, start=L1, end=L2>
<localVar:index=1 , name=a , desc=I, sig=null, start=L1, end=L2>

L1 {
return
}
L2 {
}
}

public static bridge test$default(org.guenhter.springboot.kt.Fun arg0, int arg1, int arg2, java.lang.Object arg3) { //(Lorg/guenhter/springboot/kt/Fun;IILjava/lang/Object;)V
iload2 // reference to arg2
iconst_1
iand
ifeq L1
L2 {
bipush 123 // <-- THIS IS YOUR DEFAULT VALUE
istore1 // reference to arg1
}
L1 {
aload0 // reference to arg0
iload1 // reference to arg1
invokevirtual org/guenhter/springboot/kt/Fun test((I)V);
return
}
}

public final test2() { //()V
<localVar:index=0 , name=this , desc=Lorg/guenhter/springboot/kt/Fun;, sig=null, start=L1, end=L2>

L1 {
aload0 // reference to self
iconst_0
iconst_1
aconst_null
invokestatic org/guenhter/springboot/kt/Fun test$default((Lorg/guenhter/springboot/kt/Fun;IILjava/lang/Object;)V);
}
L3 {
aload0 // reference to self
bipush 100
invokevirtual org/guenhter/springboot/kt/Fun test((I)V);
}
L4 {
return
}
L2 {
}
}

在 Java 语法中看起来像
final public class AKt {
final public static void test(int i) {
}

public static void test$default(int i, int i0, Object a) {
if ((i0 & 1) != 0) {
i = 123;
}
AKt.test(i);
}

final public static void test2() {
AKt.test$default(0, 1, (Object)null);
AKt.test(100);
}
}

所以对你来说最好的选择是将默认值提取到一个常量中:
private val DEFAULT_MIN = 1
private val DEFAULT_MAX = 1

fun DieRoll.cheatRoll():Int = roll(min = DEFAULT_MAX-1)

fun roll(min: Int = DEFAULT_MIN, max: Int = DEFAULT_MAX): Int = (min..max).rand()

关于kotlin - 在 Kotlin 中访问函数的默认参数值,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/45786399/

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