Merge bitcoin#25879: refactor: Make Join() util work with any container type

fa95315 Use new Join() helper for ListBlockFilterTypes() (MacroFake)
fa1c716 Make Join() util work with any container type (MacroFake)
faf8da3 Remove Join() helper only used in tests (MacroFake)

Pull request description:

  This allows to drop some code

ACKs for top commit:
  naumenkogs:
    ACK fa95315
  stickies-v:
    ACK [fa95315](bitcoin@fa95315)

Tree-SHA512: efd65b65722f46b221bd53140ff22bd8e45adc83617980233f28f695be3108a6ab01affd751d715134ffcb9762228ba8952e9467e590cff022c83e0f5404cb74

Author: MacroFake

src/blockfilter.cpp

@@ -3,7 +3,6 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <mutex>
-#include <sstream>
 #include <set>
 
 #include <blockfilter.h>
@@ -13,6 +12,7 @@
 #include <script/script.h>
 #include <streams.h>
 #include <util/golombrice.h>
+#include <util/string.h>
 
 /// SerType used to serialize parameters in GCS filter encoding.
 static constexpr int GCS_SER_TYPE = SER_NETWORK;
@@ -179,19 +179,7 @@ const std::set<BlockFilterType>& AllBlockFilterTypes()
 
 const std::string& ListBlockFilterTypes()
 {
-    static std::string type_list;
-
-    static std::once_flag flag;
-    std::call_once(flag, []() {
-            std::stringstream ret;
-            bool first = true;
-            for (auto entry : g_filter_types) {
-                if (!first) ret << ", ";
-                ret << entry.second;
-                first = false;
-            }
-            type_list = ret.str();
-        });
+    static std::string type_list{Join(g_filter_types, ", ", [](const auto& entry) { return entry.second; })};
 
     return type_list;
 }

src/test/util_tests.cpp

@@ -248,15 +248,15 @@ BOOST_AUTO_TEST_CASE(span_write_bytes)
 BOOST_AUTO_TEST_CASE(util_Join)
 {
     // Normal version
-    BOOST_CHECK_EQUAL(Join({}, ", "), "");
-    BOOST_CHECK_EQUAL(Join({"foo"}, ", "), "foo");
-    BOOST_CHECK_EQUAL(Join({"foo", "bar"}, ", "), "foo, bar");
+    BOOST_CHECK_EQUAL(Join(std::vector<std::string>{}, ", "), "");
+    BOOST_CHECK_EQUAL(Join(std::vector<std::string>{"foo"}, ", "), "foo");
+    BOOST_CHECK_EQUAL(Join(std::vector<std::string>{"foo", "bar"}, ", "), "foo, bar");
 
     // Version with unary operator
     const auto op_upper = [](const std::string& s) { return ToUpper(s); };
-    BOOST_CHECK_EQUAL(Join<std::string>({}, ", ", op_upper), "");
-    BOOST_CHECK_EQUAL(Join<std::string>({"foo"}, ", ", op_upper), "FOO");
-    BOOST_CHECK_EQUAL(Join<std::string>({"foo", "bar"}, ", ", op_upper), "FOO, BAR");
+    BOOST_CHECK_EQUAL(Join(std::list<std::string>{}, ", ", op_upper), "");
+    BOOST_CHECK_EQUAL(Join(std::list<std::string>{"foo"}, ", ", op_upper), "FOO");
+    BOOST_CHECK_EQUAL(Join(std::list<std::string>{"foo", "bar"}, ", ", op_upper), "FOO, BAR");
 }
 
 BOOST_AUTO_TEST_CASE(util_ReplaceAll)

src/util/string.h

@@ -58,34 +58,30 @@ void ReplaceAll(std::string& in_out, const std::string& search, const std::strin
 }
 
 /**
- * Join a list of items
+ * Join all container items. Typically used to concatenate strings but accepts
+ * containers with elements of any type.
  *
- * @param list       The list to join
- * @param separator  The separator
- * @param unary_op   Apply this operator to each item in the list
+ * @param container The items to join
+ * @param separator The separator
+ * @param unary_op  Apply this operator to each item
  */
-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)))
+template <typename C, typename S, typename UnaryOp>
+auto Join(const C& container, const S& separator, UnaryOp unary_op)
 {
-    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));
+    decltype(unary_op(*container.begin())) ret;
+    bool first{true};
+    for (const auto& item : container) {
+        if (!first) ret += separator;
+        ret += unary_op(item);
+        first = false;
     }
     return ret;
 }
 
-template <typename T, typename T2>
-T Join(const std::vector<T>& list, const T2& separator)
+template <typename C, typename S>
+auto Join(const C& container, const S& 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, std::string_view separator)
-{
-    return Join<std::string>(list, separator);
+    return Join(container, separator, [](const auto& i) { return i; });
 }
 
 /**