adding ToMap, used to create maps from iterables of entries

jnape · jnape · commit bb15b6e58633 · 2017-01-02T14:36:56.000-06:00
diff --git a/src/main/java/com/jnape/palatable/lambda/functions/builtin/fn2/ToMap.java b/src/main/java/com/jnape/palatable/lambda/functions/builtin/fn2/ToMap.java
@@ -0,0 +1,44 @@
+package com.jnape.palatable.lambda.functions.builtin.fn2;
+
+import com.jnape.palatable.lambda.functions.Fn1;
+import com.jnape.palatable.lambda.functions.Fn2;
+
+import java.util.Map;
+import java.util.function.Supplier;
+
+/**
+ * Given a {@link Supplier} of some {@link Map} <code>M</code>, create an instance of <code>M</code> and put
+ * all of the entries in the provided <code>Iterable</code> into the instance. Note that instances of <code>M</code>
+ * must support {@link Map#put} (which is to say, must not throw on invocation).
+ *
+ * @param <K> the key element type
+ * @param <V> the value element type
+ * @param <M> the resulting map type
+ */
+public final class ToMap<K, V, M extends Map<K, V>> implements Fn2<Supplier<M>, Iterable<Map.Entry<K, V>>, M> {
+
+    private static final ToMap INSTANCE = new ToMap<>();
+
+    private ToMap() {
+    }
+
+    @Override
+    public M apply(Supplier<M> mSupplier, Iterable<Map.Entry<K, V>> entries) {
+        M m = mSupplier.get();
+        entries.forEach(kv -> m.put(kv.getKey(), kv.getValue()));
+        return m;
+    }
+
+    @SuppressWarnings("unchecked")
+    public static <K, V, M extends Map<K, V>> ToMap<K, V, M> toMap() {
+        return INSTANCE;
+    }
+
+    public static <K, V, M extends Map<K, V>> Fn1<Iterable<Map.Entry<K, V>>, M> toMap(Supplier<M> mSupplier) {
+        return ToMap.<K, V, M>toMap().apply(mSupplier);
+    }
+
+    public static <K, V, M extends Map<K, V>> M toMap(Supplier<M> mSupplier, Iterable<Map.Entry<K, V>> entries) {
+        return toMap(mSupplier).apply(entries);
+    }
+}
diff --git a/src/test/java/com/jnape/palatable/lambda/functions/builtin/fn2/ToMapTest.java b/src/test/java/com/jnape/palatable/lambda/functions/builtin/fn2/ToMapTest.java
@@ -0,0 +1,25 @@
+package com.jnape.palatable.lambda.functions.builtin.fn2;
+
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static com.jnape.palatable.lambda.adt.hlist.HList.tuple;
+import static com.jnape.palatable.lambda.functions.builtin.fn2.ToMap.toMap;
+import static java.util.Arrays.asList;
+import static org.junit.Assert.assertEquals;
+
+public class ToMapTest {
+
+    @Test
+    public void collectsEntriesIntoMap() {
+        Map<String, Integer> expected = new HashMap<String, Integer>() {{
+            put("foo", 1);
+            put("bar", 2);
+            put("baz", 3);
+        }};
+
+        assertEquals(expected, toMap().apply(HashMap::new, asList(tuple("foo", 1), tuple("bar", 2), tuple("baz", 3))));
+    }
+}
