From ffcc28921aaf021d8c374556cf5d7d20dd4e407d Mon Sep 17 00:00:00 2001
From: Francois Carouge <francois.carouge@gmail.com>
Date: Wed, 26 Oct 2022 20:42:43 -0700
Subject: [PATCH] [filter] constexpr some operations

---
 include/fcarouge/internal/kalman.hpp  | 4 ++--
 include/fcarouge/internal/utility.hpp | 9 +++++----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/fcarouge/internal/kalman.hpp b/include/fcarouge/internal/kalman.hpp
index 855f81b47..24094a77e 100644
--- a/include/fcarouge/internal/kalman.hpp
+++ b/include/fcarouge/internal/kalman.hpp
@@ -84,7 +84,7 @@ struct kalman<State, Output, void, Divide, pack<UpdateTypes...>,
   using update_types = std::tuple<UpdateTypes...>;
   using prediction_types = std::tuple<PredictionTypes...>;
 
-  inline static const auto i{identity_v<matrix<state, state>>};
+  static inline const auto i{identity_v<matrix<state, state>>};
 
   state x{zero_v<state>};
   estimate_uncertainty p{identity_v<estimate_uncertainty>};
@@ -214,7 +214,7 @@ struct kalman<State, Output, Input, Divide, pack<UpdateTypes...>,
   using update_types = std::tuple<UpdateTypes...>;
   using prediction_types = std::tuple<PredictionTypes...>;
 
-  inline static const auto i{identity_v<matrix<state, state>>};
+  static inline const auto i{identity_v<matrix<state, state>>};
 
   state x{zero_v<state>};
   estimate_uncertainty p{identity_v<estimate_uncertainty>};
diff --git a/include/fcarouge/internal/utility.hpp b/include/fcarouge/internal/utility.hpp
index fe2c8ce8e..75e878e14 100644
--- a/include/fcarouge/internal/utility.hpp
+++ b/include/fcarouge/internal/utility.hpp
@@ -81,23 +81,24 @@ constexpr void for_constexpr(Function &&function) {
 }
 
 template <typename Type>
-inline const Type identity_v{
+inline constexpr Type identity_v{
     //! @todo Implement standard, default form.
 };
 
 template <arithmetic Arithmetic>
-inline const Arithmetic identity_v<Arithmetic>{1};
+inline constexpr Arithmetic identity_v<Arithmetic>{1};
 
 template <typename Matrix>
   requires requires(Matrix value) { value.Identity(); }
 inline const auto identity_v<Matrix>{Matrix::Identity()};
 
 template <typename Type>
-inline const Type zero_v{
+inline constexpr Type zero_v{
     //! @todo Implement standard, default form.
 };
 
-template <arithmetic Arithmetic> inline const Arithmetic zero_v<Arithmetic>{0};
+template <arithmetic Arithmetic>
+inline constexpr Arithmetic zero_v<Arithmetic>{0};
 
 template <typename Matrix>
   requires requires(Matrix value) { value.Zero(); }