[GitHub] [arrow] pitrou commented on a change in pull request #12448: ARROW-15700: [C++] Compilation error on Ubuntu 18.04

[GitBox <gi...@apache.org>]

pitrou commented on a change in pull request #12448:
URL: https://github.com/apache/arrow/pull/12448#discussion_r808997942



##########
File path: cpp/src/arrow/engine/substrait/expression_internal.cc
##########
@@ -443,8 +443,11 @@ struct ScalarToProtoImpl {
     return Status::OK();
   }
 
+  // Note: while std::string&& would be better for the argument
+  // type, older versions of protobuf don't have this overload
+  // yet.
   template <typename ScalarWithBufferValue>
-  Status FromBuffer(void (substrait::Expression::Literal::*set)(std::string&&),
+  Status FromBuffer(void (substrait::Expression::Literal::*set)(const std::string&),

Review comment:
       You could also take a lambda and let C++ resolve the best overload there:
   ```c++
     template <typename LitteralSetter>
     Status FromBuffer(LitteralSetter&& set_lit,
                       const ScalarWithBufferValue& scalar_with_buffer) {
       set_lit(lit_, scalar_with_buffer.value->ToString());
       return Status::OK();
     }
   
     Status Visit(const StringScalar& s) {
       return FromBuffer([](Lit* lit, std::string s) { lit->set_string(std::move(s)); });
     }
   ```




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