Add lazyMap implementation

1 files changed, 25 insertions, 0 deletions

diff --git a/src/main/java/org/zwobble/mammoth/internal/util/MammothIterables.java b/src/main/java/org/zwobble/mammoth/internal/util/MammothIterables.java
index 4335dc1..0280ac9 100644
--- a/src/main/java/org/zwobble/mammoth/internal/util/MammothIterables.java
+++ b/src/main/java/org/zwobble/mammoth/internal/util/MammothIterables.java
@@ -2,7 +2,9 @@ package org.zwobble.mammoth.internal.util;
 
 import com.google.common.collect.Iterables;
 
+import java.util.Iterator;
 import java.util.Optional;
+import java.util.function.Function;
 import java.util.function.Predicate;
 
 public class MammothIterables {
@@ -18,4 +20,27 @@ public class MammothIterables {
         }
         return Optional.empty();
     }
+
+    public static <T, R> Iterable<R> lazyMap(Iterable<T> iterable, Function<T, R> function) {
+        return new Iterable<R>() {
+            @Override
+            public Iterator<R> iterator() {
+                return map(iterable.iterator(), function);
+            }
+        };
+    }
+
+    private static <T, R> Iterator<R> map(Iterator<T> iterator, Function<T, R> function) {
+        return new Iterator<R>() {
+            @Override
+            public boolean hasNext() {
+                return iterator.hasNext();
+            }
+
+            @Override
+            public R next() {
+                return function.apply(iterator.next());
+            }
+        };
+    }
 }