From effba81d241424a4497ef8ea882eb5836f894773 Mon Sep 17 00:00:00 2001
From: Max Katz <maxpkatz@gmail.com>
Date: Sun, 6 Aug 2023 18:41:21 -0400
Subject: [PATCH] Add has_G to check if G is in the EOS type (#1303)

This fixes invocations of gamma_law with types other than eos_t.
---
 EOS/gamma_law/actual_eos.H       | 4 +++-
 EOS/primordial_chem/actual_eos.H | 4 +++-
 interfaces/eos_type.H            | 8 ++++++++
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/EOS/gamma_law/actual_eos.H b/EOS/gamma_law/actual_eos.H
index e375694403..1ca36e5b70 100644
--- a/EOS/gamma_law/actual_eos.H
+++ b/EOS/gamma_law/actual_eos.H
@@ -265,7 +265,9 @@ void actual_eos (I input, T& state)
 
             // sound speed
             state.cs = std::sqrt(eos_gamma * state.p * rhoinv);
-            state.G = 0.5 * (1.0 + eos_gamma);
+            if constexpr (has_G<T>::value) {
+                state.G = 0.5 * (1.0 + eos_gamma);
+            }
         }
     }
 
diff --git a/EOS/primordial_chem/actual_eos.H b/EOS/primordial_chem/actual_eos.H
index e268d4b69d..b5cbf1e400 100644
--- a/EOS/primordial_chem/actual_eos.H
+++ b/EOS/primordial_chem/actual_eos.H
@@ -278,7 +278,9 @@ void actual_eos (I input, T& state)
         state.dpdT = pressure / temp;
         state.dpdr = pressure / dens;
         state.cs = std::sqrt((1.0 + 1.0/sum_gammasinv) * state.p /state.rho);
-        state.G = 0.5 * (1.0 + (1.0 + 1.0/sum_gammasinv));
+        if constexpr (has_G<T>::value) {
+            state.G = 0.5 * (1.0 + (1.0 + 1.0/sum_gammasinv));
+        }
     }
 
     Real dedT = sum_gammasinv * sum_Abarinv * gasconstant;
diff --git a/interfaces/eos_type.H b/interfaces/eos_type.H
index cd4f494cfd..cdfe210a13 100644
--- a/interfaces/eos_type.H
+++ b/interfaces/eos_type.H
@@ -198,6 +198,14 @@ template <typename T>
 struct has_dpdA<T, decltype((void)T::dpdA, void())>
     : std::true_type {};
 
+template <typename T, typename Enable = void>
+struct has_G
+    : std::false_type {};
+
+template <typename T>
+struct has_G<T, decltype((void)T::G, void())>
+    : std::true_type {};
+
 template <typename T, typename Enable = void>
 struct has_dpdZ
     : std::false_type {};