Adding toCollection

jnape · jnape · commit f00ea5a471e4 · 2016-12-12T17:38:36.000-06:00
diff --git a/src/main/java/com/jnape/palatable/lambda/functions/builtin/fn1/ToCollection.java b/src/main/java/com/jnape/palatable/lambda/functions/builtin/fn1/ToCollection.java
@@ -0,0 +1,43 @@
+package com.jnape.palatable.lambda.functions.builtin.fn1;
+
+import com.jnape.palatable.lambda.functions.Fn1;
+import com.jnape.palatable.lambda.functions.Fn2;
+
+import java.util.Collection;
+import java.util.function.Supplier;
+
+/**
+ * Given a {@link Supplier} of some {@link Collection} <code>C</code>, create an instance of <code>C</code> and add
+ * all of the elements in the provided <code>Iterable</code> to the instance. Note that instances of <code>C</code>
+ * must support {@link Collection#add} (which is to say, must not throw on invocation).
+ *
+ * @param <A> the iterable element type
+ * @param <C> the resulting collection type
+ */
+public final class ToCollection<A, C extends Collection<A>> implements Fn2<Supplier<C>, Iterable<A>, C> {
+
+    private static final ToCollection INSTANCE = new ToCollection();
+
+    private ToCollection() {
+    }
+
+    @Override
+    public C apply(Supplier<C> cSupplier, Iterable<A> as) {
+        C c = cSupplier.get();
+        as.forEach(c::add);
+        return c;
+    }
+
+    @SuppressWarnings("unchecked")
+    public static <A, C extends Collection<A>> ToCollection<A, C> toCollection() {
+        return INSTANCE;
+    }
+
+    public static <A, C extends Collection<A>> Fn1<Iterable<A>, C> toCollection(Supplier<C> cSupplier) {
+        return ToCollection.<A, C>toCollection().apply(cSupplier);
+    }
+
+    public static <A, C extends Collection<A>> C toCollection(Supplier<C> cSupplier, Iterable<A> as) {
+        return toCollection(cSupplier).apply(as);
+    }
+}
diff --git a/src/test/java/com/jnape/palatable/lambda/functions/builtin/fn1/ToCollectionTest.java b/src/test/java/com/jnape/palatable/lambda/functions/builtin/fn1/ToCollectionTest.java
@@ -0,0 +1,20 @@
+package com.jnape.palatable.lambda.functions.builtin.fn1;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.function.Supplier;
+
+import static com.jnape.palatable.lambda.functions.builtin.fn1.ToCollection.toCollection;
+import static java.util.Arrays.asList;
+import static org.junit.Assert.assertEquals;
+
+public class ToCollectionTest {
+
+    @Test
+    public void convertsIterablesToCollectionInstance() {
+        Supplier<Collection<Integer>> listFactory = ArrayList::new;
+        assertEquals(asList(1, 2, 3), toCollection(listFactory, asList(1, 2, 3)));
+    }
+}
