possible solution to #567

include/gsl/gsl

@@ -25,5 +25,6 @@
 #include <gsl/span>        // span
 #include <gsl/string_span> // zstring, string_span, zstring_builder...
 #include <gsl/pointers>    // owner, not_null
+#include <gsl/pointers_ios>// ostream operator for not_null
 
 #endif // GSL_GSL_H

include/gsl/pointers

@@ -21,7 +21,6 @@
 
 #include <gsl/gsl_assert>
 
-#include <iostream>
 #include <memory>
 #include <type_traits>
 
@@ -112,13 +111,6 @@ private:
     T ptr_;
 };
 
-template <class T>
-std::ostream& operator<<(std::ostream& os, const not_null<T>& val)
-{
-    os << val.get();
-    return os;
-}
-
 template <class T, class U>
 auto operator==(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() == rhs.get())
 {

include/gsl/pointers_ios

@@ -0,0 +1,36 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#pragma once
+
+#ifndef GSL_POINTERS_IOS_H
+#define GSL_POINTERS_IOS_H
+
+#include <iostream>
+#include <gsl/pointers>
+
+namespace gsl
+{
+
+template <class T>
+std::ostream& operator<<(std::ostream& os, const not_null<T>& val)
+{
+    os << val.get();
+    return os;
+}
+
+}
+#endif