Remove MakeFunctionCall() and add test for Ternary

Change-Id: Icf798a939a9868bc66c295ef0867ec075d4860da

include/ceres/internal/expression_ref.h

diff --git a/include/ceres/internal/expression_ref.h b/include/ceres/internal/expression_ref.h
index a1afd14..570a8d8 100644
--- a/include/ceres/internal/expression_ref.h
+++ b/include/ceres/internal/expression_ref.h
@@ -110,20 +110,15 @@
 ExpressionRef operator/(ExpressionRef x, ExpressionRef y);
 
 // Functions
-
-// Helper function to create a function call expression.
-// Users can generate code for their own custom functions by adding an overload
-// for ExpressionRef that maps to MakeFunctionCall. See below for examples.
-ExpressionRef MakeFunctionCall(const std::string& name,
-                               const std::vector<ExpressionRef>& params);
-
-#define CERES_DEFINE_UNARY_FUNCTION_CALL(name) \
-  inline ExpressionRef name(ExpressionRef x) { \
-    return MakeFunctionCall(#name, {x});       \
+#define CERES_DEFINE_UNARY_FUNCTION_CALL(name)          \
+  inline ExpressionRef name(ExpressionRef x) {          \
+    return ExpressionRef::Create(                       \
+        Expression::CreateFunctionCall(#name, {x.id})); \
   }
 #define CERES_DEFINE_BINARY_FUNCTION_CALL(name)                 \
   inline ExpressionRef name(ExpressionRef x, ExpressionRef y) { \
-    return MakeFunctionCall(#name, {x, y});                     \
+    return ExpressionRef::Create(                               \
+        Expression::CreateFunctionCall(#name, {x.id, y.id}));   \
   }
 CERES_DEFINE_UNARY_FUNCTION_CALL(abs);
 CERES_DEFINE_UNARY_FUNCTION_CALL(acos);

internal/ceres/expression_ref.cc

diff --git a/internal/ceres/expression_ref.cc b/internal/ceres/expression_ref.cc
index e9cda42..8f7300c 100644
--- a/internal/ceres/expression_ref.cc
+++ b/internal/ceres/expression_ref.cc
@@ -112,20 +112,11 @@
       Expression::CreateBinaryArithmetic("*", x.id, y.id));
 }
 
-// Functions
-ExpressionRef MakeFunctionCall(const std::string& name,
-                               const std::vector<ExpressionRef>& params) {
-  std::vector<ExpressionId> ids;
-  for (auto p : params) {
-    ids.push_back(p.id);
-  }
-  return ExpressionRef::Create(Expression::CreateFunctionCall(name, ids));
-}
-
 ExpressionRef Ternary(ComparisonExpressionRef c,
                       ExpressionRef a,
                       ExpressionRef b) {
-  return MakeFunctionCall("ternary", {c.id, a.id, b.id});
+  return ExpressionRef::Create(
+      Expression::CreateFunctionCall("Ternary", {c.id, a.id, b.id}));
 }
 
 #define CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(op)                   \

internal/ceres/expression_test.cc

diff --git a/internal/ceres/expression_test.cc b/internal/ceres/expression_test.cc
index 7dd5a61..86159d9 100644
--- a/internal/ceres/expression_test.cc
+++ b/internal/ceres/expression_test.cc
@@ -115,5 +115,37 @@
   ASSERT_TRUE(graph.ExpressionForId(d.id).DirectlyDependsOn(c.id));
 }
 
+TEST(Expression, Ternary) {
+  using T = ExpressionRef;
+
+  StartRecordingExpressions();
+  T a(2);                   // 0
+  T b(3);                   // 1
+  auto c = a < b;           // 2
+  T d = Ternary(c, a, b);   // 3
+  MakeOutput(d, "result");  // 4
+  auto graph = StopRecordingExpressions();
+
+  EXPECT_EQ(graph.Size(), 5);
+
+  // Expected code
+  //   v_0 = 2;
+  //   v_1 = 3;
+  //   v_2 = v_0 < v_1;
+  //   v_3 = Ternary(v_2, v_0, v_1);
+  //   result = v_3;
+
+  ExpressionGraph reference;
+  // clang-format off
+  // Id, Type, Lhs, Value, Name, Arguments
+  reference.InsertExpression(  0,  ExpressionType::COMPILE_TIME_CONSTANT,   0,      {},        "",  2);
+  reference.InsertExpression(  1,  ExpressionType::COMPILE_TIME_CONSTANT,   1,      {},        "",  3);
+  reference.InsertExpression(  2,      ExpressionType::BINARY_COMPARISON,   2,   {0,1},       "<",  0);
+  reference.InsertExpression(  3,          ExpressionType::FUNCTION_CALL,   3, {2,0,1}, "Ternary",  0);
+  reference.InsertExpression(  4,      ExpressionType::OUTPUT_ASSIGNMENT,   4,     {3},  "result",  0);
+  // clang-format on
+  EXPECT_EQ(reference, graph);
+}
+
 }  // namespace internal
 }  // namespace ceres