From 85a502774c76e5d893a98826722574cfadd32850 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Fri, 7 Feb 2020 10:15:43 +1100
Subject: [PATCH] types: add the `convert` trait

This unconditionally replaces the first argument with the second.

It can be useful when dealing with parameter packs.
---
 types.hpp | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/types.hpp b/types.hpp
index bbe676f9..6efe638c 100644
--- a/types.hpp
+++ b/types.hpp
@@ -161,4 +161,20 @@ namespace cruft {
     //-------------------------------------------------------------------------
     template <typename ValueT>
     constexpr auto has_native_v = has_native<ValueT>::value;
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    /// Unconditionally ignore the first argument, and store the second as `type`.
+    ///
+    /// This aids converting parameter packs types. eg, converting all types
+    /// to strings by using an expression of the form:
+    ///     `convert_t<ValueT, std::string>...`
+    template <typename IgnoredT, typename ResultT>
+    struct convert {
+        using type = ResultT;
+    };
+
+
+    template <typename IgnoredT, typename ResultT>
+    using convert_t = typename convert<IgnoredT, ResultT>::type;
 }