From 6fb4e868430df2d59bc02c699b32bc93f48de830 Mon Sep 17 00:00:00 2001
From: fis <jm.yuan@outlook.com>
Date: Wed, 20 May 2020 15:53:53 +0800
Subject: [PATCH] Resolve.

---
 src/tree/param.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/tree/param.h b/src/tree/param.h
index 0831cc0db619..82eba52bb1a6 100644
--- a/src/tree/param.h
+++ b/src/tree/param.h
@@ -272,7 +272,7 @@ XGBOOST_DEVICE inline T CalcGainGivenWeight(const TrainingParams &p,
 
 // calculate the cost of loss function
 template <typename TrainingParams, typename T>
-XGBOOST_DEVICE inline T CalcGain(const TrainingParams &p, T sum_grad, T sum_hess) {
+XGBOOST_DEVICE inline T CalcGain(const TrainingParams &p, T const& sum_grad, T const& sum_hess) {
   if (sum_hess < p.min_child_weight) {
     return T(0.0);
   }
@@ -295,8 +295,8 @@ XGBOOST_DEVICE inline T CalcGain(const TrainingParams &p, T sum_grad, T sum_hess
 }
 
 template <typename TrainingParams,
-          typename StatT, typename T = decltype(StatT().GetHess())>
-XGBOOST_DEVICE inline T CalcGain(const TrainingParams &p, StatT stat) {
+          typename StatT, typename T = typename std::remove_reference< decltype(StatT().GetHess()) >::type>
+XGBOOST_DEVICE inline T CalcGain(const TrainingParams &p, StatT const& stat) {
   return CalcGain(p, stat.GetGrad(), stat.GetHess());
 }