From 8c483aa805eb3da25be685ee875555662cab1038 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?louiz=E2=80=99?= <louiz@louiz.org>
Date: Sat, 17 Mar 2018 17:33:29 +0100
Subject: Re-apply "Use if constexpr to make things a lot more readable"

This reverts commit d0e3c71b91f1a1c1780158789fd42b8ac7209495.
---
 src/database/index.hpp        | 21 +++++-----
 src/database/insert_query.hpp | 91 +++++++++++++++++++------------------------
 src/database/query.hpp        | 41 +++++++------------
 src/database/row.hpp          | 52 ++++++++++++-------------
 src/database/select_query.hpp | 77 +++++++++++++++---------------------
 src/database/table.hpp        | 44 ++++++++++-----------
 src/database/update_query.hpp | 51 +++++++++++-------------
 7 files changed, 164 insertions(+), 213 deletions(-)

diff --git a/src/database/index.hpp b/src/database/index.hpp
index 30766ab..094a36a 100644
--- a/src/database/index.hpp
+++ b/src/database/index.hpp
@@ -8,19 +8,16 @@
 namespace
 {
 template <std::size_t N=0, typename... T>
-typename std::enable_if<N == sizeof...(T), void>::type
-add_column_name(std::string&)
-{ }
-
-template <std::size_t N=0, typename... T>
-typename std::enable_if<N < sizeof...(T), void>::type
-add_column_name(std::string& out)
+void add_column_name(std::string& out)
 {
-  using ColumnType = typename std::remove_reference<decltype(std::get<N>(std::declval<std::tuple<T...>>()))>::type;
-  out += ColumnType::name;
-  if (N != sizeof...(T) - 1)
-    out += ",";
-  add_column_name<N+1, T...>(out);
+  if constexpr(N < sizeof...(T))
+    {
+      using ColumnType = typename std::remove_reference<decltype(std::get<N>(std::declval<std::tuple<T...>>()))>::type;
+      out += ColumnType::name;
+      if (N != sizeof...(T) - 1)
+        out += ",";
+      add_column_name<N + 1, T...>(out);
+    }
 }
 }
 
diff --git a/src/database/insert_query.hpp b/src/database/insert_query.hpp
index 04c098c..ed1944f 100644
--- a/src/database/insert_query.hpp
+++ b/src/database/insert_query.hpp
@@ -11,20 +11,17 @@
 #include <tuple>
 
 template <std::size_t N=0, typename... T>
-typename std::enable_if<N < sizeof...(T), void>::type
-update_autoincrement_id(std::tuple<T...>& columns, Statement& statement)
+void update_autoincrement_id(std::tuple<T...>& columns, Statement& statement)
 {
-  using ColumnType = typename std::decay<decltype(std::get<N>(columns))>::type;
-  if (std::is_same<ColumnType, Id>::value)
-    auto&& column = std::get<Id>(columns);
-  update_autoincrement_id<N+1>(columns, statement);
+  if constexpr(N < sizeof...(T))
+    {
+      using ColumnType = typename std::decay<decltype(std::get<N>(columns))>::type;
+      if (std::is_same<ColumnType, Id>::value)
+        auto&& column = std::get<Id>(columns);
+      update_autoincrement_id<N + 1>(columns, statement);
+    }
 }
 
-template <std::size_t N=0, typename... T>
-typename std::enable_if<N == sizeof...(T), void>::type
-update_autoincrement_id(std::tuple<T...>&, Statement&)
-{}
-
 struct InsertQuery: public Query
 {
   template <typename... T>
@@ -53,23 +50,20 @@ struct InsertQuery: public Query
   }
 
   template <int N=0, typename... T>
-  typename std::enable_if<N < sizeof...(T), void>::type
-  bind_param(const std::tuple<T...>& columns, Statement& statement, int index=1)
+  void bind_param(const std::tuple<T...>& columns, Statement& statement, int index=1)
   {
-    auto&& column = std::get<N>(columns);
-    using ColumnType = std::decay_t<decltype(column)>;
+    if constexpr(N < sizeof...(T))
+      {
+        auto&& column = std::get<N>(columns);
+        using ColumnType = std::decay_t<decltype(column)>;
 
-    if (!std::is_same<ColumnType, Id>::value)
-      actual_bind(statement, column.value, index++);
+        if constexpr(!std::is_same<ColumnType, Id>::value)
+          actual_bind(statement, column.value, index++);
 
-    this->bind_param<N+1>(columns, statement, index);
+        this->bind_param<N + 1>(columns, statement, index);
+      }
   }
 
-  template <int N=0, typename... T>
-  typename std::enable_if<N == sizeof...(T), void>::type
-  bind_param(const std::tuple<T...>&, Statement&, int)
-  {}
-
   template <typename... T>
   void insert_values(const std::tuple<T...>& columns)
   {
@@ -79,23 +73,21 @@ struct InsertQuery: public Query
   }
 
   template <int N=0, typename... T>
-  typename std::enable_if<N < sizeof...(T), void>::type
-  insert_value(const std::tuple<T...>& columns, int index=1)
+  void insert_value(const std::tuple<T...>& columns, int index=1)
   {
-    using ColumnType = std::decay_t<decltype(std::get<N>(columns))>;
-
-    if (!std::is_same<ColumnType, Id>::value)
+    if constexpr(N < sizeof...(T))
       {
-        this->body += "$" + std::to_string(index++);
-        if (N != sizeof...(T) - 1)
-          this->body += ", ";
+        using ColumnType = std::decay_t<decltype(std::get<N>(columns))>;
+
+        if (!std::is_same<ColumnType, Id>::value)
+          {
+            this->body += "$" + std::to_string(index++);
+            if (N != sizeof...(T) - 1)
+              this->body += ", ";
+          }
+        this->insert_value<N + 1>(columns, index);
       }
-    this->insert_value<N+1>(columns, index);
   }
-  template <int N=0, typename... T>
-  typename std::enable_if<N == sizeof...(T), void>::type
-  insert_value(const std::tuple<T...>&, const int)
-  { }
 
   template <typename... T>
   void insert_col_names(const std::tuple<T...>& columns)
@@ -106,24 +98,21 @@ struct InsertQuery: public Query
   }
 
   template <int N=0, typename... T>
-  typename std::enable_if<N < sizeof...(T), void>::type
-  insert_col_name(const std::tuple<T...>& columns)
+  void insert_col_name(const std::tuple<T...>& columns)
   {
-    using ColumnType = std::decay_t<decltype(std::get<N>(columns))>;
-
-    if (!std::is_same<ColumnType, Id>::value)
+    if constexpr(N < sizeof...(T))
       {
-        this->body += ColumnType::name;
+        using ColumnType = std::decay_t<decltype(std::get<N>(columns))>;
 
-        if (N < (sizeof...(T) - 1))
-          this->body += ", ";
-      }
+        if (!std::is_same<ColumnType, Id>::value)
+          {
+            this->body += ColumnType::name;
 
-    this->insert_col_name<N+1>(columns);
-  }
+            if (N < (sizeof...(T) - 1))
+              this->body += ", ";
+          }
 
-  template <int N=0, typename... T>
-  typename std::enable_if<N == sizeof...(T), void>::type
-  insert_col_name(const std::tuple<T...>&)
-  {}
+        this->insert_col_name<N + 1>(columns);
+      }
+  }
 };
diff --git a/src/database/query.hpp b/src/database/query.hpp
index 1c4a5ff..2a2d2d4 100644
--- a/src/database/query.hpp
+++ b/src/database/query.hpp
@@ -13,12 +13,12 @@
 
 void actual_bind(Statement& statement, const std::string& value, int index);
 void actual_bind(Statement& statement, const std::int64_t& value, int index);
-template <typename T, typename std::enable_if_t<std::is_integral<T>::value>* = 0>
+void actual_bind(Statement& statement, const std::optional<bool>& value, int index);
+template <typename T>
 void actual_bind(Statement& statement, const T& value, int index)
 {
   actual_bind(statement, static_cast<std::int64_t>(value), index);
 }
-void actual_bind(Statement& statement, const std::optional<bool>& value, int index);
 
 #ifdef DEBUG_SQL_QUERIES
 #include <utils/scopetimer.hpp>
@@ -57,38 +57,27 @@ struct Query
 #endif
 };
 
-template <typename ColumnType>
-void add_param(Query& query, const ColumnType& column)
-{
-  std::cout << "add_param<ColumnType>" << std::endl;
-  actual_add_param(query, column.value);
-}
-
+void actual_add_param(Query& query, const std::string& val);
+void actual_add_param(Query& query, const std::optional<bool>& val);
 template <typename T>
 void actual_add_param(Query& query, const T& val)
 {
   query.params.push_back(std::to_string(val));
 }
 
-void actual_add_param(Query& query, const std::string& val);
-
-template <typename T>
-typename std::enable_if<!std::is_integral<T>::value, Query&>::type
-operator<<(Query& query, const T&)
-{
-  query.body += T::name;
-  return query;
-}
-void actual_add_param(Query& query, const std::optional<bool>& val);
-
 Query& operator<<(Query& query, const char* str);
 Query& operator<<(Query& query, const std::string& str);
-template <typename Integer>
-typename std::enable_if<std::is_integral<Integer>::value, Query&>::type
-operator<<(Query& query, const Integer& i)
+template <typename T>
+Query& operator<<(Query& query, const T& i)
 {
-  query.body += "$" + std::to_string(query.current_param++);
-  actual_add_param(query, i);
+  if constexpr(std::is_integral<T>::value)
+    {
+      query.body += "$" + std::to_string(query.current_param++);
+      actual_add_param(query, i);
+    }
+  else
+    {
+      query.body += T::name;
+    }
   return query;
 }
-
diff --git a/src/database/row.hpp b/src/database/row.hpp
index 3703ff7..194a9c5 100644
--- a/src/database/row.hpp
+++ b/src/database/row.hpp
@@ -29,41 +29,39 @@ struct Row
     return col.value;
   }
 
-  template <bool Coucou=true>
-  void save(std::unique_ptr<DatabaseEngine>& db, typename std::enable_if<!is_one_of<Id, T...> && Coucou>::type* = nullptr)
+  void save(std::unique_ptr<DatabaseEngine>& db)
   {
-    this->insert(*db);
-  }
-
-  template <bool Coucou=true>
-  void save(std::unique_ptr<DatabaseEngine>& db, typename std::enable_if<is_one_of<Id, T...> && Coucou>::type* = nullptr)
-  {
-    const Id& id = std::get<Id>(this->columns);
-    if (id.value == Id::unset_value)
+    if constexpr(is_one_of<Id, T...>)
       {
-        this->insert(*db);
-        if (db->last_inserted_rowid >= 0)
-          std::get<Id>(this->columns).value = static_cast<Id::real_type>(db->last_inserted_rowid);
+        const Id& id = std::get<Id>(this->columns);
+        if (id.value == Id::unset_value)
+          {
+            this->insert(*db);
+            if (db->last_inserted_rowid >= 0)
+              std::get<Id>(this->columns).value = static_cast<Id::real_type>(db->last_inserted_rowid);
+          }
+        else
+          this->update(*db);
       }
     else
-      this->update(*db);
+      this->insert(*db);
   }
 
  private:
-  template <bool Coucou=true>
-  void insert(DatabaseEngine& db, typename std::enable_if<is_one_of<Id, T...> && Coucou>::type* = nullptr)
-  {
-    InsertQuery query(this->table_name, this->columns);
-    // Ugly workaround for non portable stuff
-    query.body += db.get_returning_id_sql_string(Id::name);
-    query.execute(db, this->columns);
-  }
-
-  template <bool Coucou=true>
-  void insert(DatabaseEngine& db, typename std::enable_if<!is_one_of<Id, T...> && Coucou>::type* = nullptr)
+  void insert(DatabaseEngine& db)
   {
-    InsertQuery query(this->table_name, this->columns);
-    query.execute(db, this->columns);
+    if constexpr(is_one_of<Id, T...>)
+      {
+        InsertQuery query(this->table_name, this->columns);
+        // Ugly workaround for non portable stuff
+        query.body += db.get_returning_id_sql_string(Id::name);
+        query.execute(db, this->columns);
+      }
+    else
+      {
+        InsertQuery query(this->table_name, this->columns);
+        query.execute(db, this->columns);
+      }
   }
 
   void update(DatabaseEngine& db)
diff --git a/src/database/select_query.hpp b/src/database/select_query.hpp
index cd9943c..f7496a4 100644
--- a/src/database/select_query.hpp
+++ b/src/database/select_query.hpp
@@ -15,48 +15,37 @@
 using namespace std::string_literals;
 
 template <typename T>
-typename std::enable_if<std::is_integral<T>::value, std::int64_t>::type
-extract_row_value(Statement& statement, const int i)
+auto extract_row_value(Statement& statement, const int i)
 {
-  return statement.get_column_int64(i);
-}
-
-template <typename T>
-typename std::enable_if<std::is_same<std::string, T>::value, T>::type
-extract_row_value(Statement& statement, const int i)
-{
-  return statement.get_column_text(i);
-}
-
-template <typename T>
-typename std::enable_if<std::is_same<std::optional<bool>, T>::value, T>::type
-extract_row_value(Statement& statement, const int i)
-{
-  const auto integer = statement.get_column_int(i);
-  if (integer > 0)
-    return true;
-  else if (integer < 0)
-    return false;
-  return std::nullopt;
+  if constexpr(std::is_integral<T>::value)
+    return statement.get_column_int64(i);
+  else if constexpr (std::is_same<std::string, T>::value)
+    return statement.get_column_text(i);
+  else if (std::is_same<std::optional<bool>, T>::value)
+    {
+      const auto integer = statement.get_column_int(i);
+      if (integer > 0)
+        return std::optional<bool>{true};
+      else if (integer < 0)
+        return std::optional<bool>{false};
+      return std::optional<bool>{};
+    }
 }
 
 template <std::size_t N=0, typename... T>
-typename std::enable_if<N < sizeof...(T), void>::type
-extract_row_values(Row<T...>& row, Statement& statement)
+void extract_row_values(Row<T...>& row, Statement& statement)
 {
-  using ColumnType = typename std::remove_reference<decltype(std::get<N>(row.columns))>::type;
+  if constexpr(N < sizeof...(T))
+    {
+      using ColumnType = typename std::remove_reference<decltype(std::get<N>(row.columns))>::type;
 
-  auto&& column = std::get<N>(row.columns);
-  column.value = static_cast<decltype(column.value)>(extract_row_value<typename ColumnType::real_type>(statement, N));
+      auto&& column = std::get<N>(row.columns);
+      column.value = static_cast<decltype(column.value)>(extract_row_value<typename ColumnType::real_type>(statement, N));
 
-  extract_row_values<N+1>(row, statement);
+      extract_row_values<N + 1>(row, statement);
+    }
 }
 
-template <std::size_t N=0, typename... T>
-typename std::enable_if<N == sizeof...(T), void>::type
-extract_row_values(Row<T...>&, Statement&)
-{}
-
 template <typename... T>
 struct SelectQuery: public Query
 {
@@ -69,23 +58,21 @@ struct SelectQuery: public Query
     }
 
     template <std::size_t N=0>
-    typename std::enable_if<N < sizeof...(T), void>::type
-    insert_col_name()
+    void insert_col_name()
     {
-      using ColumnsType = std::tuple<T...>;
-      using ColumnType = typename std::remove_reference<decltype(std::get<N>(std::declval<ColumnsType>()))>::type;
+      if constexpr(N < sizeof...(T))
+        {
+          using ColumnsType = std::tuple<T...>;
+          using ColumnType = typename std::remove_reference<decltype(std::get<N>(std::declval<ColumnsType>()))>::type;
 
-      this->body += " " + std::string{ColumnType::name};
+          this->body += " " + std::string{ColumnType::name};
 
-      if (N < (sizeof...(T) - 1))
-        this->body += ", ";
+          if (N < (sizeof...(T) - 1))
+            this->body += ", ";
 
-      this->insert_col_name<N+1>();
+          this->insert_col_name<N + 1>();
+        }
     }
-    template <std::size_t N=0>
-    typename std::enable_if<N == sizeof...(T), void>::type
-    insert_col_name()
-    {}
 
   SelectQuery& where()
     {
diff --git a/src/database/table.hpp b/src/database/table.hpp
index 680e7cc..eb68418 100644
--- a/src/database/table.hpp
+++ b/src/database/table.hpp
@@ -93,36 +93,32 @@ class Table
  private:
 
   template <std::size_t N=0>
-  typename std::enable_if<N < sizeof...(T), void>::type
-  add_column_if_not_exists(DatabaseEngine& db, const std::set<std::string>& existing_columns)
+  void add_column_if_not_exists(DatabaseEngine& db, const std::set<std::string>& existing_columns)
   {
-    using ColumnType = typename std::remove_reference<decltype(std::get<N>(std::declval<ColumnTypes>()))>::type;
-    if (existing_columns.count(ColumnType::name) == 0)
-      add_column_to_table<ColumnType>(db, this->name);
-    add_column_if_not_exists<N+1>(db, existing_columns);
+    if constexpr(N < sizeof...(T))
+      {
+        using ColumnType = typename std::remove_reference<decltype(std::get<N>(std::declval<ColumnTypes>()))>::type;
+        if (existing_columns.count(ColumnType::name) == 0)
+          add_column_to_table<ColumnType>(db, this->name);
+        add_column_if_not_exists<N + 1>(db, existing_columns);
+      }
   }
-  template <std::size_t N=0>
-  typename std::enable_if<N == sizeof...(T), void>::type
-  add_column_if_not_exists(DatabaseEngine&, const std::set<std::string>&)
-  {}
 
   template <std::size_t N=0>
-  typename std::enable_if<N < sizeof...(T), void>::type
-  add_column_create(DatabaseEngine& db, std::string& str)
+  void add_column_create(DatabaseEngine& db, std::string& str)
   {
-    using ColumnType = typename std::remove_reference<decltype(std::get<N>(std::declval<ColumnTypes>()))>::type;
-    str += ColumnType::name;
-    str += " ";
-    str += ToSQLType<ColumnType>(db);
-    if (N != sizeof...(T) - 1)
-      str += ",";
-
-    add_column_create<N+1>(db, str);
+    if constexpr(N < sizeof...(T))
+      {
+        using ColumnType = typename std::remove_reference<decltype(std::get<N>(std::declval<ColumnTypes>()))>::type;
+        str += ColumnType::name;
+        str += " ";
+        str += ToSQLType<ColumnType>(db);
+        if (N != sizeof...(T) - 1)
+          str += ",";
+
+        add_column_create<N + 1>(db, str);
+      }
   }
-  template <std::size_t N=0>
-  typename std::enable_if<N == sizeof...(T), void>::type
-  add_column_create(DatabaseEngine&, std::string&)
-  { }
 
   const std::string name;
 };
diff --git a/src/database/update_query.hpp b/src/database/update_query.hpp
index a29ac3f..0ee2bd9 100644
--- a/src/database/update_query.hpp
+++ b/src/database/update_query.hpp
@@ -39,27 +39,25 @@ struct UpdateQuery: public Query
   }
 
   template <int N=0, typename... T>
-  typename std::enable_if<N < sizeof...(T), void>::type
-  insert_col_name_and_value(const std::tuple<T...>& columns)
+  void insert_col_name_and_value(const std::tuple<T...>& columns)
   {
-    using ColumnType = std::decay_t<decltype(std::get<N>(columns))>;
-
-    if (!std::is_same<ColumnType, Id>::value)
+    if constexpr(N < sizeof...(T))
       {
-        this->body += ColumnType::name + "=$"s + std::to_string(this->current_param);
-        this->current_param++;
+        using ColumnType = std::decay_t<decltype(std::get<N>(columns))>;
 
-        if (N < (sizeof...(T) - 1))
-          this->body += ", ";
-      }
+        if (!std::is_same<ColumnType, Id>::value)
+          {
+            this->body += ColumnType::name + "=$"s
+                          + std::to_string(this->current_param);
+            this->current_param++;
 
-    this->insert_col_name_and_value<N+1>(columns);
-  }
-  template <int N=0, typename... T>
-  typename std::enable_if<N == sizeof...(T), void>::type
-  insert_col_name_and_value(const std::tuple<T...>&)
-  {}
+            if (N < (sizeof...(T) - 1))
+              this->body += ", ";
+          }
 
+        this->insert_col_name_and_value<N + 1>(columns);
+      }
+  }
 
   template <typename... T>
   void execute(DatabaseEngine& db, const std::tuple<T...>& columns)
@@ -76,23 +74,20 @@ struct UpdateQuery: public Query
   }
 
   template <int N=0, typename... T>
-  typename std::enable_if<N < sizeof...(T), void>::type
-  bind_param(const std::tuple<T...>& columns, Statement& statement, int index=1)
+  void bind_param(const std::tuple<T...>& columns, Statement& statement, int index=1)
   {
-    auto&& column = std::get<N>(columns);
-    using ColumnType = std::decay_t<decltype(column)>;
+    if constexpr(N < sizeof...(T))
+      {
+        auto&& column = std::get<N>(columns);
+        using ColumnType = std::decay_t<decltype(column)>;
 
-    if (!std::is_same<ColumnType, Id>::value)
-      actual_bind(statement, column.value, index++);
+        if (!std::is_same<ColumnType, Id>::value)
+          actual_bind(statement, column.value, index++);
 
-    this->bind_param<N+1>(columns, statement, index);
+        this->bind_param<N + 1>(columns, statement, index);
+      }
   }
 
-  template <int N=0, typename... T>
-  typename std::enable_if<N == sizeof...(T), void>::type
-  bind_param(const std::tuple<T...>&, Statement&, int)
-  {}
-
   template <typename... T>
   void bind_id(const std::tuple<T...>& columns, Statement& statement)
   {
-- 
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