├── .gitignore ├── LICENSE.txt ├── README.md ├── pom.xml └── src ├── main └── java │ └── com │ └── benjiweber │ └── typeref │ ├── DefaultValue.java │ ├── MethodAwareConsumer.java │ ├── MethodAwareFunction.java │ ├── MethodAwarePredicate.java │ ├── MethodFinder.java │ ├── NameOf.java │ ├── NamedValue.java │ ├── Newable.java │ ├── NewableConsumer.java │ ├── Parameters.java │ └── TypeReference.java └── test └── java └── com └── benjiweber ├── DefaultValuesAndMethodReferences.java ├── Examples.java ├── HashLiteralExample.java ├── MethodFinderExample.java └── PuppetExample.java /.gitignore: -------------------------------------------------------------------------------- 1 | target/ 2 | *.class 3 | *.iml 4 | .idea/ 5 | 6 | -------------------------------------------------------------------------------- /LICENSE.txt: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. 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We also recommend that a 185 | file or class name and description of purpose be included on the 186 | same "printed page" as the copyright notice for easier 187 | identification within third-party archives. 188 | 189 | Copyright {yyyy} {name of copyright owner} 190 | 191 | Licensed under the Apache License, Version 2.0 (the "License"); 192 | you may not use this file except in compliance with the License. 193 | You may obtain a copy of the License at 194 | 195 | http://www.apache.org/licenses/LICENSE-2.0 196 | 197 | Unless required by applicable law or agreed to in writing, software 198 | distributed under the License is distributed on an "AS IS" BASIS, 199 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 200 | See the License for the specific language governing permissions and 201 | limitations under the License. 202 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # lambda-type-references 2 | 3 | Type references using lambdas 4 | 5 | http://benjiweber.com/blog/2015/08/04/lambda-type-references/ 6 | 7 | ```java 8 | public static T create(TypeReference type) { 9 | return type.newInstance(); 10 | } 11 | @Test 12 | public void creating_a_list() { 13 | ArrayList list = create(i->i); 14 | list.add("hello"); 15 | list.add("world"); 16 | 17 | assertEquals(asList("hello","world"), list); 18 | } 19 | 20 | @Test 21 | public void creating_a_map() { 22 | HashMap map = create(i->i); 23 | map.put("hello",1); 24 | map.put("world",2); 25 | 26 | assertEquals(Integer.valueOf(1), map.get("hello")); 27 | assertEquals(Integer.valueOf(2), map.get("world")); 28 | } 29 | 30 | @Test 31 | public void variable_ref() { 32 | TypeReference ref = i->i; 33 | assertEquals("java.lang.String", ref.type().getName()); 34 | } 35 | 36 | @Test 37 | public void variable_ref_generic_type() { 38 | TypeReference> ref = i->i; 39 | ArrayList strings = ref.newInstance(); 40 | assertEquals(Collections.emptyList(), strings); 41 | } 42 | 43 | @Test 44 | public void parameter_object() { 45 | List result = foo(list -> { 46 | list.add("Hello"); 47 | list.add("World"); 48 | }); 49 | 50 | assertEquals(asList("Hello foo", "World foo"), result); 51 | } 52 | 53 | public static List foo(Parameters> params) { 54 | return params.get().stream().map(s -> s + " foo").collect(toList()); 55 | } 56 | ``` -------------------------------------------------------------------------------- /pom.xml: -------------------------------------------------------------------------------- 1 | 2 | 5 | 4.0.0 6 | 7 | com.benjiweber 8 | lambda-type-references 9 | 1.0-SNAPSHOT 10 | 11 | 12 | 13 | org.apache.maven.plugins 14 | maven-compiler-plugin 15 | 16 | 1.8 17 | 1.8 18 | 19 | 20 | 21 | 22 | 23 | 24 | junit 25 | junit 26 | 4.11 27 | 28 | 29 | org.mockito 30 | mockito-all 31 | 1.9.5 32 | 33 | 34 | -------------------------------------------------------------------------------- /src/main/java/com/benjiweber/typeref/DefaultValue.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber.typeref; 2 | 3 | import java.util.HashMap; 4 | import java.util.Map; 5 | 6 | public class DefaultValue { 7 | private static Map, Object> defaultValues = new HashMap<>(); 8 | static { 9 | defaultValues.put(int.class, 0); 10 | defaultValues.put(Integer.class, 0); 11 | defaultValues.put(boolean.class, false); 12 | defaultValues.put(Boolean.class, false); 13 | defaultValues.put(byte.class, (byte)0); 14 | defaultValues.put(Byte.class, 0); 15 | defaultValues.put(char.class, ' '); 16 | defaultValues.put(Character.class, ' '); 17 | defaultValues.put(short.class, (short)0.0); 18 | defaultValues.put(Short.class, (short)0.0); 19 | defaultValues.put(long.class, 0l); 20 | defaultValues.put(Long.class, 0L); 21 | defaultValues.put(float.class, 0.0f); 22 | defaultValues.put(Float.class, 0.0f); 23 | defaultValues.put(double.class, 0.0d); 24 | defaultValues.put(Double.class, 0.0d); 25 | } 26 | 27 | public static T ofType(Class type) { 28 | return (T) defaultValues.getOrDefault(type, null); 29 | } 30 | } 31 | -------------------------------------------------------------------------------- /src/main/java/com/benjiweber/typeref/MethodAwareConsumer.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber.typeref; 2 | 3 | import java.util.function.Consumer; 4 | import java.util.function.Function; 5 | 6 | public interface MethodAwareConsumer extends Consumer, MethodFinder { } 7 | -------------------------------------------------------------------------------- /src/main/java/com/benjiweber/typeref/MethodAwareFunction.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber.typeref; 2 | 3 | import java.util.function.Consumer; 4 | import java.util.function.Function; 5 | import java.util.function.Predicate; 6 | 7 | public interface MethodAwareFunction extends Function, MethodFinder { } -------------------------------------------------------------------------------- /src/main/java/com/benjiweber/typeref/MethodAwarePredicate.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber.typeref; 2 | 3 | import java.util.function.Consumer; 4 | import java.util.function.Predicate; 5 | 6 | public interface MethodAwarePredicate extends Predicate, MethodFinder { } -------------------------------------------------------------------------------- /src/main/java/com/benjiweber/typeref/MethodFinder.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber.typeref; 2 | 3 | import java.io.Serializable; 4 | import java.lang.invoke.SerializedLambda; 5 | import java.lang.reflect.Method; 6 | import java.lang.reflect.Parameter; 7 | import java.util.Objects; 8 | 9 | import static java.util.Arrays.asList; 10 | 11 | public interface MethodFinder extends Serializable { 12 | default SerializedLambda serialized() { 13 | try { 14 | Method replaceMethod = getClass().getDeclaredMethod("writeReplace"); 15 | replaceMethod.setAccessible(true); 16 | return (SerializedLambda) replaceMethod.invoke(this); 17 | } catch (Exception e) { 18 | throw new RuntimeException(e); 19 | } 20 | } 21 | 22 | default Class getContainingClass() { 23 | try { 24 | String className = serialized().getImplClass().replaceAll("/", "."); 25 | return Class.forName(className); 26 | } catch (Exception e) { 27 | throw new RuntimeException(e); 28 | } 29 | } 30 | 31 | default Method method() { 32 | SerializedLambda lambda = serialized(); 33 | Class containingClass = getContainingClass(); 34 | return asList(containingClass.getDeclaredMethods()) 35 | .stream() 36 | .filter(method -> Objects.equals(method.getName(), lambda.getImplMethodName())) 37 | .findFirst() 38 | .orElseThrow(UnableToGuessMethodException::new); 39 | } 40 | 41 | default Parameter parameter(int n) { 42 | return method().getParameters()[n]; 43 | } 44 | 45 | default Object defaultValueForParameter(int n) { 46 | return DefaultValue.ofType(parameter(n).getType()); 47 | } 48 | 49 | class UnableToGuessMethodException extends RuntimeException {} 50 | } 51 | -------------------------------------------------------------------------------- /src/main/java/com/benjiweber/typeref/NameOf.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber.typeref; 2 | 3 | import com.benjiweber.typeref.NewableConsumer; 4 | 5 | import java.util.function.Consumer; 6 | 7 | public class NameOf { 8 | public static void main(String... args) { 9 | new NameOf().aMethod(null); 10 | } 11 | public void aMethod(String aParam) { 12 | throw new NullPointerException(nameof(this::aMethod, 0)); 13 | } 14 | 15 | public static String nameof(NewableConsumer method, int arg) { 16 | try { 17 | StackTraceElement caller = new Throwable().fillInStackTrace().getStackTrace()[1]; 18 | Class cls = Class.forName(caller.getClassName()); 19 | return cls.getDeclaredMethod(caller.getMethodName(), method.type()).getParameters()[arg].getName(); 20 | } catch (Exception e) { 21 | throw new RuntimeException(e); 22 | } 23 | } 24 | } 25 | -------------------------------------------------------------------------------- /src/main/java/com/benjiweber/typeref/NamedValue.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber.typeref; 2 | 3 | import java.util.Objects; 4 | import java.util.function.Function; 5 | 6 | public interface NamedValue extends MethodFinder, Function { 7 | default String name() { 8 | checkParametersEnabled(); 9 | return parameter(0).getName(); 10 | } 11 | default void checkParametersEnabled() { 12 | if (Objects.equals("arg0", parameter(0).getName())) { 13 | throw new IllegalStateException("You need to compile with javac -parameters for parameter reflection to work; You also need java 8u60 or newer to use it with lambdas"); 14 | } 15 | } 16 | 17 | default T value() { 18 | return apply(name()); 19 | } 20 | } 21 | -------------------------------------------------------------------------------- /src/main/java/com/benjiweber/typeref/Newable.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber.typeref; 2 | 3 | public interface Newable extends MethodFinder { 4 | default Class type() { 5 | return (Class)parameter(0).getType(); 6 | } 7 | default T newInstance() { 8 | try { 9 | return type().newInstance(); 10 | } catch (Exception e) { 11 | throw new RuntimeException(e); 12 | } 13 | } 14 | } 15 | -------------------------------------------------------------------------------- /src/main/java/com/benjiweber/typeref/NewableConsumer.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber.typeref; 2 | 3 | import java.util.function.Consumer; 4 | 5 | public interface NewableConsumer extends Consumer, Newable {} 6 | -------------------------------------------------------------------------------- /src/main/java/com/benjiweber/typeref/Parameters.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber.typeref; 2 | 3 | public interface Parameters extends NewableConsumer { 4 | default T get() { 5 | T t = newInstance(); 6 | accept(t); 7 | return t; 8 | } 9 | } -------------------------------------------------------------------------------- /src/main/java/com/benjiweber/typeref/TypeReference.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber.typeref; 2 | 3 | import java.util.function.Consumer; 4 | 5 | public interface TypeReference extends Newable { 6 | T typeIs(T t); 7 | default Consumer consumer() { 8 | return this::typeIs; 9 | } 10 | } 11 | -------------------------------------------------------------------------------- /src/test/java/com/benjiweber/DefaultValuesAndMethodReferences.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber; 2 | 3 | import com.benjiweber.typeref.DefaultValue; 4 | import com.benjiweber.typeref.MethodAwareConsumer; 5 | import org.junit.Test; 6 | import org.junit.runner.RunWith; 7 | import org.mockito.Mock; 8 | import org.mockito.runners.MockitoJUnitRunner; 9 | 10 | import static org.mockito.Mockito.verify; 11 | import static org.mockito.Mockito.verifyNoMoreInteractions; 12 | 13 | @RunWith(MockitoJUnitRunner.class) 14 | public class DefaultValuesAndMethodReferences { 15 | 16 | @Mock UsesPrimitives mock; 17 | 18 | public interface UsesPrimitives { 19 | void takesInt(int i); 20 | void takesLong(long l); 21 | void takesShort(short s); 22 | void takesBoolean(boolean b); 23 | void takesChar(char c); 24 | void takesFloat(float f); 25 | void takesDouble(double d); 26 | } 27 | 28 | @Test(expected = NullPointerException.class) 29 | public void passing_null_throws_npe() { 30 | MethodAwareConsumer f = mock::takesInt; 31 | f.accept(null); 32 | } 33 | 34 | @Test 35 | public void int_param() { 36 | check(mock::takesInt, () -> verify(mock).takesInt(0)); 37 | } 38 | 39 | @Test 40 | public void longParam() { 41 | check(mock::takesLong, () -> verify(mock).takesLong(0L)); 42 | } 43 | 44 | @Test 45 | public void shortParam() { 46 | check(mock::takesShort, () -> verify(mock).takesShort((short)0.0)); 47 | } 48 | 49 | @Test 50 | public void booleanParam() { 51 | check(mock::takesBoolean, () -> verify(mock).takesBoolean(false)); 52 | } 53 | 54 | @Test 55 | public void charParam() { 56 | check(mock::takesChar, () -> verify(mock).takesChar(' ')); 57 | } 58 | 59 | @Test 60 | public void floatParam() { 61 | check(mock::takesFloat, () -> verify(mock).takesFloat(0.0f)); 62 | } 63 | 64 | @Test 65 | public void doubleParam() { 66 | check(mock::takesDouble, () -> verify(mock).takesDouble(0.0)); 67 | } 68 | 69 | private void check(MethodAwareConsumer consumer, Runnable verification) { 70 | consumer.accept(DefaultValue.ofType(consumer.parameter(0).getType())); 71 | verification.run(); 72 | verifyNoMoreInteractions(mock); 73 | } 74 | } 75 | -------------------------------------------------------------------------------- /src/test/java/com/benjiweber/Examples.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber; 2 | 3 | import com.benjiweber.typeref.Parameters; 4 | import com.benjiweber.typeref.TypeReference; 5 | import org.junit.Test; 6 | 7 | import java.util.ArrayList; 8 | import java.util.Collections; 9 | import java.util.HashMap; 10 | import java.util.List; 11 | import java.util.function.Function; 12 | 13 | import static java.util.Arrays.asList; 14 | import static java.util.stream.Collectors.toList; 15 | import static org.junit.Assert.assertEquals; 16 | 17 | public class Examples { 18 | public static T create(TypeReference type) { 19 | return type.newInstance(); 20 | } 21 | @Test 22 | public void creating_a_list() { 23 | ArrayList list = create(i->i); 24 | list.add("hello"); 25 | list.add("world"); 26 | 27 | assertEquals(asList("hello","world"), list); 28 | } 29 | 30 | @Test 31 | public void creating_a_map() { 32 | HashMap map = create(i->i); 33 | map.put("hello",1); 34 | map.put("world",2); 35 | 36 | assertEquals(Integer.valueOf(1), map.get("hello")); 37 | assertEquals(Integer.valueOf(2), map.get("world")); 38 | } 39 | 40 | @Test 41 | public void variable_ref() { 42 | TypeReference ref = i->i; 43 | assertEquals("java.lang.String", ref.type().getName()); 44 | } 45 | 46 | @Test 47 | public void variable_ref_generic_type() { 48 | TypeReference> ref = i->i; 49 | ArrayList strings = ref.newInstance(); 50 | assertEquals(Collections.emptyList(), strings); 51 | } 52 | 53 | @Test 54 | public void parameter_object() { 55 | List result = foo(list -> { 56 | list.add("Hello"); 57 | list.add("World"); 58 | }); 59 | 60 | assertEquals(asList("Hello foo", "World foo"), result); 61 | } 62 | 63 | public static List foo(Parameters> params) { 64 | return params.get().stream().map(s -> s + " foo").collect(toList()); 65 | } 66 | public static void foo(String aAparam) { 67 | Function f = bobBobBob -> "hello"; 68 | f.apply((String)(Object)5); 69 | } 70 | 71 | 72 | } 73 | -------------------------------------------------------------------------------- /src/test/java/com/benjiweber/HashLiteralExample.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber; 2 | 3 | import com.benjiweber.typeref.NamedValue; 4 | import org.junit.Test; 5 | 6 | import java.util.HashMap; 7 | import java.util.Map; 8 | 9 | import static java.util.Arrays.asList; 10 | import static org.junit.Assert.assertEquals; 11 | 12 | public class HashLiteralExample { 13 | @Test 14 | public void java_hash_literal() { 15 | Map hash = hash( 16 | hello -> "world", 17 | bob -> bob, 18 | bill -> "was here" 19 | ); 20 | 21 | assertEquals("world", hash.get("hello")); 22 | assertEquals("bob", hash.get("bob")); 23 | assertEquals("was here", hash.get("bill")); 24 | } 25 | 26 | public static Map hash(NamedValue... keyValuePairs) { 27 | Map map = new HashMap<>(); 28 | asList(keyValuePairs) 29 | .stream() 30 | .forEach(kvp -> 31 | map.put( 32 | kvp.name(), 33 | kvp.value()) 34 | ); 35 | return map; 36 | } 37 | } 38 | -------------------------------------------------------------------------------- /src/test/java/com/benjiweber/MethodFinderExample.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber; 2 | 3 | import com.benjiweber.typeref.MethodAwarePredicate; 4 | import org.hamcrest.CoreMatchers; 5 | import org.junit.Test; 6 | 7 | import java.lang.reflect.InvocationTargetException; 8 | import java.lang.reflect.Method; 9 | 10 | import static org.hamcrest.CoreMatchers.startsWith; 11 | import static org.junit.Assert.*; 12 | 13 | public class MethodFinderExample { 14 | 15 | @Test 16 | public void find_lambda_synthetic_method() { 17 | MethodAwarePredicate p = s -> s.toLowerCase().equals("hello"); 18 | assertEquals(MethodFinderExample.class.getName(), p.method().getDeclaringClass().getName()); 19 | assertThat(p.method().getName(), startsWith("lambda$find_lambda_synthetic_method$")); 20 | } 21 | 22 | @Test 23 | public void execute_lambda_synthetic_method() throws NoSuchMethodException, ClassNotFoundException, InvocationTargetException, IllegalAccessException { 24 | Runnable r = () -> { 25 | try { 26 | MethodAwarePredicate p = i -> i < 5; 27 | 28 | assertFalse((Boolean) p.method().invoke(null, 5)); 29 | assertTrue((Boolean) p.method().invoke(null, 3)); 30 | } catch (Exception e) { 31 | throw new RuntimeException(e); 32 | } 33 | }; 34 | r.run(); 35 | } 36 | 37 | 38 | } 39 | -------------------------------------------------------------------------------- /src/test/java/com/benjiweber/PuppetExample.java: -------------------------------------------------------------------------------- 1 | package com.benjiweber; 2 | 3 | import com.benjiweber.typeref.NamedValue; 4 | import org.junit.Test; 5 | 6 | import static java.util.Arrays.asList; 7 | import static org.junit.Assert.assertEquals; 8 | 9 | public class PuppetExample { 10 | 11 | 12 | @Test 13 | public void puppet_example() { 14 | String manifest = new Apache().toString(); 15 | assertEquals( 16 | "class Apache {\n" + 17 | "\n" + 18 | "\tfile{\n" + 19 | "\t\tname\t=> \"/etc/httpd/httpd.conf\",\n" + 20 | "\t\tsource\t=> template(\"httpd.tpl\"),\n" + 21 | "\t\towner\t=> root,\n" + 22 | "\t\tgroup\t=> root,\n" + 23 | "\t}\n" + 24 | "\tcron{\n" + 25 | "\t\tname\t=> \"logrotate\",\n" + 26 | "\t\tcommand\t=> \"/usr/sbin/logrotate\",\n" + 27 | "\t\tuser\t=> root,\n" + 28 | "\t\thour\t=> \"2\",\n" + 29 | "\t\tminute\t=> \"*/10\",\n" + 30 | "\t}\n" + 31 | "\n" + 32 | "}", 33 | manifest 34 | ); 35 | } 36 | 37 | 38 | static class Apache extends PuppetClass {{ 39 | file( 40 | name -> "/etc/httpd/httpd.conf", 41 | source -> template("httpd.tpl"), 42 | owner -> root, 43 | group -> root 44 | ); 45 | 46 | cron ( 47 | name -> "logrotate", 48 | command -> "/usr/sbin/logrotate", 49 | user -> root, 50 | hour -> "2", 51 | minute -> "*/10" 52 | ); 53 | }} 54 | 55 | interface PuppetParam extends NamedValue { 56 | default String asString() { 57 | return name() + "\t=> " + quote(value()); 58 | } 59 | default String quote(Object value) { 60 | return value instanceof String 61 | ? "\"" + value + "\"" 62 | : value.toString(); 63 | } 64 | } 65 | 66 | interface PuppetType { 67 | StringBuilder builder(); 68 | default void append(String type, PuppetParam... params) { 69 | builder().append("\n\t"); 70 | builder().append(type).append("{\n"); 71 | asList(params) 72 | .stream() 73 | .map(PuppetParam::asString) 74 | .map(value -> "\t\t" + value + ",\n") 75 | .forEach(builder()::append); 76 | builder().append("\t}"); 77 | } 78 | } 79 | interface PuppetFile extends PuppetType { 80 | default void file(PuppetParam... params) { 81 | append("file", params); 82 | } 83 | } 84 | interface PuppetCron extends PuppetType { 85 | default void cron(PuppetParam... params) { 86 | append("cron", params); 87 | } 88 | } 89 | public static class PuppetClass implements PuppetFile, PuppetCron { 90 | StringBuilder builder = new StringBuilder(); 91 | 92 | public StringBuilder builder() { 93 | return builder; 94 | } 95 | 96 | static PuppetLiteral template(String name) { 97 | return new PuppetLiteral("template(\"" + name + "\")"); 98 | } 99 | 100 | static PuppetLiteral root = new PuppetLiteral("root"); 101 | 102 | @Override 103 | public String toString() { 104 | builder.insert(0, "class " + getClass().getSimpleName() + " {\n"); 105 | builder.append("\n\n}"); 106 | return builder.toString(); 107 | 108 | } 109 | } 110 | 111 | static class PuppetLiteral { 112 | String value; 113 | 114 | public PuppetLiteral(String value) { 115 | this.value = value; 116 | } 117 | 118 | @Override 119 | public String toString() { 120 | return value; 121 | } 122 | } 123 | } 124 | 125 | --------------------------------------------------------------------------------