feat: Function支持特定索引参数的函数，避免编写不关注的变量名

Author: lokic

src/main/java/com/github/lokic/javaplus/functional/function/Function2.java

@@ -1,6 +1,16 @@
 package com.github.lokic.javaplus.functional.function;
 
+import java.util.function.Function;
+
 @FunctionalInterface
 public interface Function2<T1, T2, R> {
     R apply(T1 t1, T2 t2);
+
+    static <T1, T2, R> Function2<T1, T2, R> $1(Function<T1, R> function) {
+        return (t1, t2) -> function.apply(t1);
+    }
+
+    static <T1, T2, R> Function2<T1, T2, R> $2(Function<T2, R> function) {
+        return (t1, t2) -> function.apply(t2);
+    }
 }

src/main/java/com/github/lokic/javaplus/functional/function/Function3.java

@@ -1,6 +1,20 @@
 package com.github.lokic.javaplus.functional.function;
 
+import java.util.function.Function;
+
 @FunctionalInterface
 public interface Function3<T1, T2, T3, R> {
     R apply(T1 t1, T2 t2, T3 t3);
+
+    static <T1, T2, T3, R> Function3<T1, T2, T3, R> $1(Function<T1, R> function) {
+        return (t1, t2, t3) -> function.apply(t1);
+    }
+
+    static <T1, T2, T3, R> Function3<T1, T2, T3, R> $2(Function<T2, R> function) {
+        return (t1, t2, t3) -> function.apply(t2);
+    }
+
+    static <T1, T2, T3, R> Function3<T1, T2, T3, R> $3(Function<T3, R> function) {
+        return (t1, t2, t3) -> function.apply(t3);
+    }
 }

src/main/java/com/github/lokic/javaplus/functional/function/Function4.java

@@ -1,6 +1,24 @@
 package com.github.lokic.javaplus.functional.function;
 
+import java.util.function.Function;
+
 @FunctionalInterface
 public interface Function4<T1, T2, T3, T4, R> {
     R apply(T1 t1, T2 t2, T3 t3, T4 t4);
+
+    static <T1, T2, T3, T4, R> Function4<T1, T2, T3, T4, R> $1(Function<T1, R> function) {
+        return (t1, t2, t3, t4) -> function.apply(t1);
+    }
+
+    static <T1, T2, T3, T4, R> Function4<T1, T2, T3, T4, R> $2(Function<T2, R> function) {
+        return (t1, t2, t3, t4) -> function.apply(t2);
+    }
+
+    static <T1, T2, T3, T4, R> Function4<T1, T2, T3, T4, R> $3(Function<T3, R> function) {
+        return (t1, t2, t3, t4) -> function.apply(t3);
+    }
+
+    static <T1, T2, T3, T4, R> Function4<T1, T2, T3, T4, R> $4(Function<T4, R> function) {
+        return (t1, t2, t3, t4) -> function.apply(t4);
+    }
 }

src/main/java/com/github/lokic/javaplus/functional/function/Function5.java

@@ -1,6 +1,28 @@
 package com.github.lokic.javaplus.functional.function;
 
+import java.util.function.Function;
+
 @FunctionalInterface
 public interface Function5<T1, T2, T3, T4, T5, R> {
     R apply(T1 t1, T2 t2, T3 t3, T4 t4, T5 t5);
+
+    static <T1, T2, T3, T4, T5, R> Function5<T1, T2, T3, T4, T5, R> $1(Function<T1, R> function) {
+        return (t1, t2, t3, t4, t5) -> function.apply(t1);
+    }
+
+    static <T1, T2, T3, T4, T5, R> Function5<T1, T2, T3, T4, T5, R> $2(Function<T2, R> function) {
+        return (t1, t2, t3, t4, t5) -> function.apply(t2);
+    }
+
+    static <T1, T2, T3, T4, T5, R> Function5<T1, T2, T3, T4, T5, R> $3(Function<T3, R> function) {
+        return (t1, t2, t3, t4, t5) -> function.apply(t3);
+    }
+
+    static <T1, T2, T3, T4, T5, R> Function5<T1, T2, T3, T4, T5, R> $4(Function<T4, R> function) {
+        return (t1, t2, t3, t4, t5) -> function.apply(t4);
+    }
+
+    static <T1, T2, T3, T4, T5, R> Function5<T1, T2, T3, T4, T5, R> $5(Function<T5, R> function) {
+        return (t1, t2, t3, t4, t5) -> function.apply(t5);
+    }
 }

src/main/java/com/github/lokic/javaplus/functional/function/Function6.java

@@ -1,6 +1,32 @@
 package com.github.lokic.javaplus.functional.function;
 
+import java.util.function.Function;
+
 @FunctionalInterface
 public interface Function6<T1, T2, T3, T4, T5, T6, R> {
     R apply(T1 t1, T2 t2, T3 t3, T4 t4, T5 t5, T6 t6);
+
+    static <T1, T2, T3, T4, T5, T6, R> Function6<T1, T2, T3, T4, T5, T6, R> $1(Function<T1, R> function) {
+        return (t1, t2, t3, t4, t5, t6) -> function.apply(t1);
+    }
+
+    static <T1, T2, T3, T4, T5, T6, R> Function6<T1, T2, T3, T4, T5, T6, R> $2(Function<T2, R> function) {
+        return (t1, t2, t3, t4, t5, t6) -> function.apply(t2);
+    }
+
+    static <T1, T2, T3, T4, T5, T6, R> Function6<T1, T2, T3, T4, T5, T6, R> $3(Function<T3, R> function) {
+        return (t1, t2, t3, t4, t5, t6) -> function.apply(t3);
+    }
+
+    static <T1, T2, T3, T4, T5, T6, R> Function6<T1, T2, T3, T4, T5, T6, R> $4(Function<T4, R> function) {
+        return (t1, t2, t3, t4, t5, t6) -> function.apply(t4);
+    }
+
+    static <T1, T2, T3, T4, T5, T6, R> Function6<T1, T2, T3, T4, T5, T6, R> $5(Function<T5, R> function) {
+        return (t1, t2, t3, t4, t5, t6) -> function.apply(t5);
+    }
+
+    static <T1, T2, T3, T4, T5, T6, R> Function6<T1, T2, T3, T4, T5, T6, R> $6(Function<T6, R> function) {
+        return (t1, t2, t3, t4, t5, t6) -> function.apply(t6);
+    }
 }