add swap.hpp

Author: robertshepherdcpp

mlib.vcxproj

@@ -168,6 +168,7 @@
     <ClInclude Include="string_parse.hpp" />
     <ClInclude Include="sub_pack.hpp" />
     <ClInclude Include="sub_tuple.hpp" />
+    <ClInclude Include="swap.hpp" />
     <ClInclude Include="times.hpp" />
     <ClInclude Include="trait.hpp" />
     <ClInclude Include="transform.hpp" />

mlib.vcxproj.filters

@@ -159,6 +159,9 @@
     <ClInclude Include="tuple_equal.hpp">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="swap.hpp">
+      <Filter>Header Files</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="Main.cpp">

swap.hpp

@@ -0,0 +1,56 @@
+#include<cstddef> // std::size_t
+#include<utility> // std::index_sequence
+#include<tuple>   // std::tuple
+
+#include"get_nth_element.hpp"
+
+namespace mlib
+{
+    // a class to hold compile time data
+    template<auto... Ts>
+    struct container
+    {
+        template<auto X>
+        constexpr auto get()
+        {
+            return mlib::get_nth_element<X>(Ts...);
+        }
+    };
+
+    // this is a compile time parameter that is easy to pass into things
+    template<auto X>
+    struct c_p__
+    {
+    };
+
+    // when condition(value) returns TrueValue, else returns FalseValue
+    template<auto value, auto condition, auto other_condition, auto TrueValue, auto SecondTrueValue, auto FalseValue>
+    struct when_
+    {
+        constexpr auto operator()()
+        {
+            if constexpr (condition(value))
+            {
+                return TrueValue;
+            }
+            if constexpr (other_condition(value))
+            {
+                return SecondTrueValue;
+            }
+            else
+            {
+                return FalseValue(c_p__<value>{});
+            }
+        }
+    };
+
+    // this function swaps Index and Other index then returns the tuple.
+    template<auto Index, auto OtherIndex, auto... Ts>
+    constexpr auto swap() // -> container
+    {
+        return[&]<std::size_t... indexes>(std::index_sequence<indexes...>)
+        {
+            return container < (when_ < indexes, [=](auto x) {return x == Index; }, [=](auto x) {return x == OtherIndex; }, mlib::get_nth_element<OtherIndex>(Ts...), mlib::get_nth_element<Index>(Ts...), [=]<auto X>(c_p__<X>) { return mlib::get_nth_element<X>(Ts...); } > {}())... > {};
+        }(std::make_index_sequence<sizeof...(Ts)>{});
+    }
+} // namespace mlib