Lmbda: A Java repository from leosarra

Lmbda

This is library that can be used to generate lambdas from method handles. This includes methods, constructors, field accessors (getter, setter, even for final fields) and any other MethodHandle that can be constructed.

How to use

Every available MethodHandle can be implemented by a functional interface. But only if the two method signatures match. Object types will be auto casted to the target type if possible, the same goes for boxing/unboxing of primitive types.

Non static methods will always take a extra parameter which represents the target object of the method. This is always the first parameter.

Note: Generating functions requires that you have access to the target class. In Java 9, this is even more important because the module your code is located in must be able to access the module of the target class, see MethodHandles#privateLookupIn for more info.

Generating method functions

Static setter method

Consider the following class which holds a static setter function.

class MyObject {
    private static void set(int value) {
        // ...
    }
}

If you want to generate a function for the static set(int) method, you need to use a interface which takes one parameter (value) and return void to reflect the method signature. The IntConsumer is a good choice available within the Java 8 API.

class MyClass {
    
    void test() throws Exception {
        final MethodHandles.Lookup lookup = MethodHandlesX.privateLookupIn(MyObject.class, MethodHandles.lookup());
        final MethodHandle methodHandle = lookup.findStatic(MyObject.class, "set", MethodType.methodType(void.class, int.class));

        final IntConsumer setter = LmbdaFactory.create(LmbdaType.of(IntConsumer.class), methodHandle);
        setter.accept(1000);
    }
}

Setter method

Consider the following class which holds a setter function.

class MyObject {
    private void set(int value) {
        // ...
    }
}

If you want to generate a function for the static set(int) method, you need to use a interface which takes two parameters:

The target of where the method is declared, this will be the target object on which the method is invoked. E.g. target.set(value)
The value that will be passed to the set method.

the first one is the target where the method is declared, MyObject (value) and return void to reflect the method signature. The ObjIntConsumer is a good choice available within the Java 8 API.

class MyClass {
    
    void test() throws Exception {
        final MethodHandles.Lookup lookup = MethodHandlesX.privateLookupIn(MyObject.class, MethodHandles.lookup());
        final MethodHandle methodHandle = lookup.findVirtual(MyObject.class, "set", MethodType.methodType(void.class, int.class));

        final ObjIntConsumer<MyObject> setter = LmbdaFactory.create(new LmbdaType<ObjIntConsumer<MyObject>>() {}, methodHandle);
        
        final MyObject myObject = new MyObject();
        setter.accept(myObject, 1000);
    }
    
}

Benchmarks

Below you can find a few benchmarks. lmbda will be generated at runtime, all the other ones are implemented manually. The generated structure of the lmbda is almost the same as the static_mh.

The following benchmark implements a lambda function to access a int field, a ToIntFunction is implemented in this case to avoid boxing/unboxing.

Benchmark	Mode	Cnt	Score	Error	Units
IntGetterFieldBenchmark.dynamic_mh	avgt	15	3.891	± 0.450	ns/op
IntGetterFieldBenchmark.dynamic_reflect	avgt	15	4.788	± 0.205	ns/op
IntGetterFieldBenchmark.lmbda	avgt	15	1.988	± 0.061	ns/op
IntGetterFieldBenchmark.plain	avgt	15	1.969	± 0.049	ns/op
IntGetterFieldBenchmark.static_mh	avgt	15	1.935	± 0.021	ns/op
IntGetterFieldBenchmark.static_reflect	avgt	15	3.912	± 0.007	ns/op

This benchmark returns a Integer through the getValue method from a target object.