add mallocator module

src/basic_string/internal/mallocator.d

@@ -0,0 +1,46 @@
+module basic_string.internal.mallocator;
+
+
+
+//mallocator:
+version(D_BetterC){
+    public struct Mallocator{
+        import std.experimental.allocator.common : platformAlignment;
+
+        enum uint alignment = platformAlignment;
+
+        static void[] allocate(size_t bytes)@trusted @nogc nothrow pure{
+            import core.memory : pureMalloc;
+            if (!bytes) return null;
+            auto p = pureMalloc(bytes);
+            return p ? p[0 .. bytes] : null;
+        }
+
+        static bool deallocate(void[] b)@system @nogc nothrow pure{
+            import core.memory : pureFree;
+            pureFree(b.ptr);
+            return true;
+        }
+
+        static bool reallocate(ref void[] b, size_t s)@system @nogc nothrow pure{
+            import core.memory : pureRealloc;
+            if (!s){
+                // fuzzy area in the C standard, see http://goo.gl/ZpWeSE
+                // so just deallocate and nullify the pointer
+                deallocate(b);
+                b = null;
+                return true;
+            }
+
+            auto p = cast(ubyte*) pureRealloc(b.ptr, s);
+            if (!p) return false;
+            b = p[0 .. s];
+            return true;
+        }
+
+        static Mallocator instance;
+    }
+}
+else{
+    public import std.experimental.allocator.mallocator : Mallocator;
+}