Add sformat() writing to an output range

source/tanya/range/adapter.d

@@ -3,9 +3,9 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 /**
- * Range adapters.
+ * Range adapters transform some data structures into ranges.
  *
- * Copyright: Eugene Wissner 2018.
+ * Copyright: Eugene Wissner 2018-2019.
  * License: $(LINK2 https://www.mozilla.org/en-US/MPL/2.0/,
  *                  Mozilla Public License, v. 2.0).
  * Authors: $(LINK2 mailto:info@caraus.de, Eugene Wissner)
@@ -13,3 +13,53 @@
  *                 tanya/range/adapter.d)
  */
 module tanya.range.adapter;
+
+import tanya.functional;
+import tanya.meta.trait;
+import tanya.range;
+
+version (unittest)
+{
+    static struct Container
+    {
+        void insertBack(const(char)[])
+        {
+        }
+    }
+}
+
+package (tanya) auto backInserter(Container)(return ref Container container)
+if (hasMember!(Container, "insertBack"))
+{
+    static struct BackInserter
+    {
+        private Container* container;
+
+        this(ref Container container) @trusted
+        {
+            this.container = &container;
+        }
+
+        void opCall(T)(auto ref T data)
+        {
+            this.container.insertBack(forward!data);
+        }
+    }
+    return BackInserter(container);
+}
+
+@nogc nothrow pure @safe unittest
+{
+    auto func()()
+    {
+        Container container;
+        return backInserter(container);
+    }
+    static assert(!is(typeof(func!())));
+}
+
+@nogc nothrow pure @safe unittest
+{
+    Container container;
+    static assert(isOutputRange!(typeof(backInserter(container)), string));
+}