Merge #20736: rpc: Replace boost::variant with std::variant for RPCArg.m_fallback

fa749fbea3cad64582f76f7a58cfcc0d91a97326 rpc: Replace boost::variant with std::variant for RPCArg.m_fallback (MarcoFalke)

Pull request description:

  Now that we can use std::variant from the vanilla standard library, drop the third-party boost variant dependency.

  Patch is split out from #20480. A step-by-step replacement is possible because we don't have our own `Variant` wrapper and the source code specifies `boost::variant` explicitly.
  I think a step-by-step replacement should be preferred, because it simplifies review.

ACKs for top commit:
  fjahr:
    re-ACK fa749fbea3cad64582f76f7a58cfcc0d91a97326
  Sjors:
    re-ACK fa749fbea3cad64582f76f7a58cfcc0d91a97326

Tree-SHA512: 5e3c12b7d535f73065b4afa8df0a488f78fb25d2234f5ecbf740e624db03a34c35fea100eb7d37e84741721310e6450b7fb4296a2207a7ed1fa24485b3650981

1 files changed, 6 insertions, 6 deletions

diff --git a/src/rpc/util.cpp b/src/rpc/util.cpp
index 1b21587b6d..e377a80fbd 100644
--- a/src/rpc/util.cpp
+++ b/src/rpc/util.cpp
@@ -1,4 +1,4 @@
-// Copyright (c) 2017-2020 The Bitcoin Core developers
+// Copyright (c) 2017-2021 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -562,10 +562,10 @@ std::string RPCArg::GetName() const
 
 bool RPCArg::IsOptional() const
 {
-    if (m_fallback.which() == 1) {
+    if (m_fallback.index() == 1) {
         return true;
     } else {
-        return RPCArg::Optional::NO != boost::get<RPCArg::Optional>(m_fallback);
+        return RPCArg::Optional::NO != std::get<RPCArg::Optional>(m_fallback);
     }
 }
 
@@ -609,10 +609,10 @@ std::string RPCArg::ToDescriptionString() const
         }
         } // no default case, so the compiler can warn about missing cases
     }
-    if (m_fallback.which() == 1) {
-        ret += ", optional, default=" + boost::get<std::string>(m_fallback);
+    if (m_fallback.index() == 1) {
+        ret += ", optional, default=" + std::get<std::string>(m_fallback);
     } else {
-        switch (boost::get<RPCArg::Optional>(m_fallback)) {
+        switch (std::get<RPCArg::Optional>(m_fallback)) {
         case RPCArg::Optional::OMITTED: {
             // nothing to do. Element is treated as if not present and has no default value
             break;