Const connection config (#494)

- The postgres connection does not change the connection_config thus passing it as const.
- Implies 'thread safety' when using the same config for multiple connections

Co-authored-by: Carel Combrink <carel.combrink@vastech.co.za>

tests/postgresql/usage/BasicConstConfig.cpp

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2017, Volker Aßmann
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ *  * Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+ * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <iostream>
+#include <memory>
+#include <stdexcept>
+
+#include <sqlpp11/postgresql/connection.h>
+#include <sqlpp11/postgresql/exception.h>
+#include <sqlpp11/sqlpp11.h>
+
+namespace sql = sqlpp::postgresql;
+int BasicConstConfig(int, char*[])
+{
+  const std::shared_ptr<const sql::connection_config> const_config = []()
+  {
+    auto config = std::make_shared<sql::connection_config>();
+    config->host = "localhost";
+    config->user = "unknown_user_must_fail";
+    return config;
+  }();
+
+  try
+  {
+    sql::connection db(const_config);
+
+    throw std::logic_error("should never reach this point");
+  }
+  catch (const sqlpp::postgresql::broken_connection& ex)
+  {
+    std::cout << "Got exception: '" << ex.what() << "'";
+    return 0;
+  }
+
+  return 1;
+}