define geometry::get_or (#59)

Change-Id: Ib981ae0cceea84b385f43a0d25cf8ae7b3f6bdd0

geometry/BUILD.bazel

@@ -42,6 +42,7 @@ cc_library(
     srcs = [
         "src/algebra.hpp",
         "src/algebra_core.hpp",
+        "src/algebra_fwd.hpp",
         "src/algebra_type.hpp",
         "src/blade_base.hpp",
         "src/blade_list.hpp",
@@ -62,6 +63,7 @@ cc_library(
         "src/exterior_product.hpp",
         "src/geometric_product.hpp",
         "src/get.hpp",
+        "src/get_or.hpp",
         "src/multivector_base.hpp",
         "src/multivector_for.hpp",
         "src/regressive_product.hpp",

geometry/geometry.hpp

@@ -1,13 +1,15 @@
 #pragma once
 
 #include "geometry/src/algebra.hpp"
+#include "geometry/src/algebra_fwd.hpp"
 #include "geometry/src/algebra_type.hpp"
 #include "geometry/src/common_algebra_type.hpp"
 #include "geometry/src/dual.hpp"
 #include "geometry/src/equality_comparison.hpp"
 #include "geometry/src/exterior_product.hpp"
 #include "geometry/src/geometric_product.hpp"
 #include "geometry/src/get.hpp"
+#include "geometry/src/get_or.hpp"
 #include "geometry/src/multivector_for.hpp"
 #include "geometry/src/regressive_product.hpp"
 #include "geometry/src/sum.hpp"

geometry/src/algebra.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "geometry/src/algebra_core.hpp"
+#include "geometry/src/algebra_fwd.hpp"
 #include "geometry/src/detail/algebra_reference_constant.hpp"
 #include "geometry/src/detail/is_constexpr_scalar_type.hpp"
 #include "geometry/type_metaprogramming.hpp"
@@ -107,28 +108,6 @@ struct algebra
   using dual_algebra_type = algebra<S, N, not Dual>;
 };
 
-namespace detail {
-
-template <class T>
-struct is_algebra : std::false_type
-{};
-template <class S, std::size_t N, bool Dual>
-struct is_algebra<algebra<S, N, Dual>> : std::true_type
-{};
-
-}  // namespace detail
-
-/// check if T is a specialization of algebra
-///
-/// @{
-template <class T>
-struct is_algebra : detail::is_algebra<std::remove_cv_t<T>>
-{};
-
-template <class T>
-inline constexpr auto is_algebra_v = is_algebra<T>::value;
-/// @}
-
 /// @name helper type aliases and values
 /// @{
 

geometry/src/algebra_core.hpp

@@ -6,6 +6,7 @@
 #include "geometry/src/detail/ordered.hpp"
 #include "geometry/src/detail/strictly_increasing.hpp"
 #include "geometry/src/get.hpp"
+#include "geometry/src/get_or.hpp"
 #include "geometry/src/multivector_base.hpp"
 #include "geometry/type_metaprogramming.hpp"
 

geometry/src/algebra_fwd.hpp

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <cstddef>
+#include <type_traits>
+
+namespace geometry {
+
+template <class S, std::size_t N, bool Dual>
+struct algebra;
+
+namespace detail {
+
+template <class T>
+struct is_algebra : std::false_type
+{};
+template <class S, std::size_t N, bool Dual>
+struct is_algebra<algebra<S, N, Dual>> : std::true_type
+{};
+
+}  // namespace detail
+
+/// check if T is a specialization of algebra
+///
+/// @{
+template <class T>
+struct is_algebra : detail::is_algebra<std::remove_cv_t<T>>
+{};
+
+template <class T>
+inline constexpr auto is_algebra_v = is_algebra<T>::value;
+/// @}
+
+}  // namespace geometry

geometry/src/common_algebra_type.hpp

@@ -1,6 +1,6 @@
 #pragma once
 
-#include "geometry/src/algebra.hpp"
+#include "geometry/src/algebra_fwd.hpp"
 #include "geometry/src/algebra_type.hpp"
 
 #include <type_traits>

geometry/src/get.hpp

@@ -1,7 +1,5 @@
 #pragma once
 
-#include "geometry/src/algebra_type.hpp"
-#include "geometry/src/blade_base.hpp"
 #include "geometry/src/multivector_base.hpp"
 
 #include <type_traits>

geometry/src/get_or.hpp

@@ -0,0 +1,39 @@
+#pragma once
+
+#include "geometry/src/blade_base.hpp"
+#include "geometry/src/common_algebra_type.hpp"
+#include "geometry/src/multivector_base.hpp"
+
+#include <type_traits>
+#include <utility>
+
+namespace geometry {
+namespace detail {
+
+template <class T>
+auto get_or() -> void = delete;
+
+struct get_or_fn
+{
+  template <
+      class V,
+      class B,
+      class = std::enable_if_t<
+          is_multivector_v<V> and is_blade_v<B>,
+          common_algebra_type_t<V, B>>>
+  constexpr decltype(auto) operator()(const V & v, const B & value) const
+  {
+    return get_or(v, value);
+  }
+};
+
+}  // namespace detail
+
+inline namespace cpo {
+
+/// access a blade of a multivector or return a default value
+///
+inline constexpr auto get_or = detail::get_or_fn{};
+
+}  // namespace cpo
+}  // namespace geometry

test/algebra_get_test.cpp

@@ -124,4 +124,14 @@ auto main() -> int
 
     return expect(true);
   };
+
+  "get_or multivector"_ctest = [] {
+    const auto x = 2 * e<> + 3 * e<0>;
+
+    using ::skytest::eq;
+    return expect(                         //
+        eq(2 * e<>, get_or(x, e<>)) and    //
+        eq(3 * e<0>, get_or(x, e<0>)) and  //
+        eq(e<1>, get_or(x, e<1>)));
+  };
 }