@def proposal

1-DefExample.java

import lombok.Def;
import java.util.Optional;
import com.google.common.collect.ImmutableMap;

public class DefExample {

	public static void main(String[] args) {
		System.out.println("All defaults:");
		foo(1, 2);
		System.out.println();

		System.out.println("Overriding a couple defaults:");
		foo(1, 2, ImmutableMap.of("d", "not default!", "e", false));
		System.out.println();

		System.out.println("Passing all parameters:");
		Optional<String> g = Optional.of("not default!");
		foo(1, 2, 3, "4", false, 5.0, g);
	}

	private static void foo(int a, int b, @Def("99") int c, @Def("default") String d, @Def("true") boolean e, @Def("99.9") double f,
				@Def Optional<String> g) {
		System.out.println("a: "+a);
		System.out.println("b: "+b);
		System.out.println("c: "+c);
		System.out.println("d: "+d);
		System.out.println("e: "+e);
		System.out.println("f: "+f);
		System.out.println("g: "+g.orElse("was not passed"));
	}

}

2-Result.md

When you compile DefExample.java with this fork of lombok in the classpath, it will automatically inject the correct two methods seen below into the same class file.

javac -cp lombok.jar:guava.jar DefExample.java

private static void foo(int a, int b) {
  foo(a, b, 99, "default", true, 99.9, Optional.empty());
}

private static void foo(int a, int b, final java.util.Map<String, Object> paramsMap) {
	foo(a, 
		b, 
		paramsMap.containsKey("c") ? (int)paramsMap.get("c") : 99, 
		paramsMap.containsKey("d") ? (String)paramsMap.get("d") : "default", 
		paramsMap.containsKey("e") ? (boolean)paramsMap.get("e") : true, 
		paramsMap.containsKey("f") ? (double)paramsMap.get("f") : 99.9, 
		paramsMap.containsKey("g") ? (Optional<String>)paramsMap.get("g") : Optional.empty());
}

Now you can run DefExample:

java -cp <path to DefExample.class>:guava.jar DefExample

All defaults:
a: 1
b: 2
c: 99
d: default
e: true
f: 99.9
g: was not passed

Overriding a couple defaults:
a: 1
b: 2
c: 99
d: not default!
e: false
f: 99.9
g: was not passed

Passing all parameters:
a: 1
b: 2
c: 3
d: 4
e: false
f: 5.0
g: not default!

@Def can be used on all primitives (except for char), as well as Strings and Java 8 Optionals. If using Optionals, no default value needs to be provided, as Optional.empty() will automatically be used.