rev: remove stmt from sqlite; shared -> unique

changes per #522 (comment)
and #522 (comment).

include/geopackage/NGen_SQLite.hpp

@@ -22,7 +22,7 @@ struct sqlite_deleter
 /**
  * Smart pointer (shared) type for sqlite3 prepared statements
  */
-using stmt_t = std::shared_ptr<sqlite3_stmt>;
+using stmt_t = std::unique_ptr<sqlite3_stmt, sqlite_deleter>;
 
 /**
  * SQLite3 row iterator
@@ -77,11 +77,6 @@ class sqlite_iter
      */
     sqlite_iter& restart();
 
-    /**
-     * Call the row iterator destructor
-     */
-    void close();
-
     /**
      * Get the current row index for the iterator
      * 
@@ -158,7 +153,6 @@ class sqlite
     using sqlite_t = std::unique_ptr<sqlite3, sqlite_deleter>;
 
     sqlite_t conn = nullptr;
-    stmt_t   stmt = nullptr;
 
   public:
     sqlite() = delete;

src/geopackage/read.cpp

@@ -19,7 +19,8 @@ std::shared_ptr<geojson::FeatureCollection> geopackage::read(
         std::string errmsg = "[" + std::string(sqlite3_errmsg(db.connection())) + "] " +
                              "table " + layer + " does not exist.\n\tTables: ";
 
-        auto errquery = db.query("SELECT name FROM sqlite_master WHERE type='table'").next();
+        auto errquery = db.query("SELECT name FROM sqlite_master WHERE type='table'");
+        errquery.next();
         while(!errquery.done()) {
             errmsg += errquery.get<std::string>(0);
             errmsg += ", ";

src/geopackage/sqlite/database.cpp

@@ -60,8 +60,7 @@ sqlite_iter sqlite::query(const std::string& statement)
         throw sqlite_error("sqlite3_prepare_v2", code, "(query: " + statement + ")");
     }
 
-    this->stmt = stmt_t(stmt, sqlite_deleter{});
-    return sqlite_iter(this->stmt);
+    return sqlite_iter(std::move(stmt_t(stmt)));
 }
 
 sqlite_iter sqlite::query(const std::string& statement, const std::vector<std::string>& binds)
@@ -83,8 +82,7 @@ sqlite_iter sqlite::query(const std::string& statement, const std::vector<std::s
         }
     }
 
-    this->stmt        = stmt_t(stmt, sqlite_deleter{});
-    return sqlite_iter(this->stmt);
+    return sqlite_iter(std::move(stmt_t(stmt)));
 }
 
 template<typename... T>
@@ -106,6 +104,5 @@ inline sqlite_iter sqlite::query(const std::string& statement, T const&... param
         }
     }
 
-    this->stmt        = stmt_t(stmt, sqlite_deleter{});
-    return sqlite_iter(this->stmt);
+    return sqlite_iter(std::move(stmt_t(stmt)));
 }

src/geopackage/sqlite/iterator.cpp

@@ -1,4 +1,5 @@
 #include <algorithm>
+#include <memory>
 
 #include "NGen_SQLite.hpp"
 
@@ -22,7 +23,7 @@ const auto sqlite_get_done_error = std::runtime_error(
 );
 
 sqlite_iter::sqlite_iter(stmt_t stmt)
-  : stmt(stmt)
+    : stmt(std::move(stmt))
 {
     // sqlite3_column_type requires the last result code to be
     // SQLITE_ROW, so we need to iterate on the first row.
@@ -39,7 +40,7 @@ sqlite_iter::sqlite_iter(stmt_t stmt)
     }
 
     this->restart();
-};
+}
 
 sqlite3_stmt* sqlite_iter::ptr() const noexcept
 {
@@ -92,11 +93,6 @@ sqlite_iter& sqlite_iter::restart()
     return *this;
 }
 
-void sqlite_iter::close()
-{
-    this->~sqlite_iter();
-}
-
 int sqlite_iter::current_row() const noexcept
 {
     return this->iteration_step;