Use unique_ptr<> for connection_pool::pimpl_

Also don't duplicate connection_pool ctor and dtor in POSIX and Windows
branches as they are exactly the same for both of them.

No real changes.

include/soci/connection-pool.h

@@ -11,6 +11,7 @@
 #include "soci/soci-platform.h"
 // std
 #include <cstddef>
+#include <memory>
 
 namespace soci
 {
@@ -31,7 +32,7 @@ public:
 
 private:
     struct connection_pool_impl;
-    connection_pool_impl * pimpl_;
+    std::unique_ptr<connection_pool_impl> pimpl_;
 
     SOCI_NOT_COPYABLE(connection_pool)
 };

src/core/connection-pool.cpp

@@ -98,16 +98,6 @@ struct connection_pool::connection_pool_impl : connection_pool_base_impl
     pthread_cond_t cond_;
 };
 
-connection_pool::connection_pool(std::size_t size)
-{
-    pimpl_ = new connection_pool_impl(size);
-}
-
-connection_pool::~connection_pool()
-{
-    delete pimpl_;
-}
-
 bool connection_pool::try_lease(std::size_t & pos, int timeout)
 {
     struct timespec tm;
@@ -242,16 +232,6 @@ struct connection_pool::connection_pool_impl : connection_pool_base_impl
     HANDLE sem_;
 };
 
-connection_pool::connection_pool(std::size_t size)
-{
-    pimpl_ = new connection_pool_impl(size);
-}
-
-connection_pool::~connection_pool()
-{
-    delete pimpl_;
-}
-
 bool connection_pool::try_lease(std::size_t & pos, int timeout)
 {
     DWORD cc = WaitForSingleObject(pimpl_->sem_,
@@ -308,6 +288,13 @@ void connection_pool::give_back(std::size_t pos)
 
 #endif // _WIN32
 
+connection_pool::connection_pool(std::size_t size)
+               : pimpl_(std::make_unique<connection_pool_impl>(size))
+{
+}
+
+connection_pool::~connection_pool() = default;
+
 session & connection_pool::at(std::size_t pos)
 {
     if (pos >= pimpl_->sessions_.size())