From 4c9b9a4882e68835f16a52f1f0657efe47e589b5 Mon Sep 17 00:00:00 2001
From: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>
Date: Sat, 9 May 2020 14:45:47 +0300
Subject: [PATCH] util: Enhance Join()

---
 src/util/string.h | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/util/string.h b/src/util/string.h
index b8e2a0623..cdb41630c 100644
--- a/src/util/string.h
+++ b/src/util/string.h
@@ -30,10 +30,11 @@ NODISCARD inline std::string TrimString(const std::string& str, const std::strin
  * @param separator  The separator
  * @param unary_op   Apply this operator to each item in the list
  */
-template <typename T, typename UnaryOp>
-std::string Join(const std::vector<T>& list, const std::string& separator, UnaryOp unary_op)
+template <typename T, typename BaseType, typename UnaryOp>
+auto Join(const std::vector<T>& list, const BaseType& separator, UnaryOp unary_op)
+    -> decltype(unary_op(list.at(0)))
 {
-    std::string ret;
+    decltype(unary_op(list.at(0))) ret;
     for (size_t i = 0; i < list.size(); ++i) {
         if (i > 0) ret += separator;
         ret += unary_op(list.at(i));
@@ -41,9 +42,16 @@ std::string Join(const std::vector<T>& list, const std::string& separator, Unary
     return ret;
 }
 
+template <typename T>
+T Join(const std::vector<T>& list, const T& separator)
+{
+    return Join(list, separator, [](const T& i) { return i; });
+}
+
+// Explicit overload needed for c_str arguments, which would otherwise cause a substitution failure in the template above.
 inline std::string Join(const std::vector<std::string>& list, const std::string& separator)
 {
-    return Join(list, separator, [](const std::string& i) { return i; });
+    return Join<std::string>(list, separator);
 }
 
 /**