[core] Privatize Interpolate<T>

2 files changed, 30 insertions, 102 deletions

diff --git a/include/mbgl/style/expression/interpolate.hpp b/include/mbgl/style/expression/interpolate.hpp
index 1a98189e29..dcdfa302ba 100644
--- a/include/mbgl/style/expression/interpolate.hpp
+++ b/include/mbgl/style/expression/interpolate.hpp
@@ -79,74 +79,11 @@ protected:
     const std::map<double, std::unique_ptr<Expression>> stops;
 };
 
-template <typename T>
-class Interpolate : public InterpolateBase {
-public:
-    Interpolate(type::Type type_,
-          Interpolator interpolator_,
-          std::unique_ptr<Expression> input_,
-          std::map<double, std::unique_ptr<Expression>> stops_
-    ) : InterpolateBase(std::move(type_), std::move(interpolator_), std::move(input_), std::move(stops_))
-    {
-        static_assert(util::Interpolatable<T>::value, "Interpolate expression requires an interpolatable value type.");
-    }
-    
-    EvaluationResult evaluate(const EvaluationContext& params) const override {
-        const EvaluationResult evaluatedInput = input->evaluate(params);
-        if (!evaluatedInput) {
-            return evaluatedInput.error();
-        }
-
-        float x = *fromExpressionValue<float>(*evaluatedInput);
-        if (std::isnan(x)) {
-            return EvaluationError { "Input is not a number." };
-        }
-
-        if (stops.empty()) {
-            return EvaluationError { "No stops in exponential curve." };
-        }
-
-        auto it = stops.upper_bound(x);
-        if (it == stops.end()) {
-            return stops.rbegin()->second->evaluate(params);
-        } else if (it == stops.begin()) {
-            return stops.begin()->second->evaluate(params);
-        } else {
-            float t = interpolationFactor({ std::prev(it)->first, it->first }, x);
-            
-            if (t == 0.0f) {
-                return std::prev(it)->second->evaluate(params);
-            }
-            if (t == 1.0f) {
-                return it->second->evaluate(params);
-            }
-            
-            EvaluationResult lower = std::prev(it)->second->evaluate(params);
-            if (!lower) {
-                return lower.error();
-            }
-            EvaluationResult upper = it->second->evaluate(params);
-            if (!upper) {
-                return upper.error();
-            }
-
-            if (!lower->is<T>()) {
-                return EvaluationError {
-                    "Expected value to be of type " + toString(valueTypeToExpressionType<T>()) +
-                    ", but found " + toString(typeOf(*lower)) + " instead."
-                };
-            }
-            
-            if (!upper->is<T>()) {
-                return EvaluationError {
-                    "Expected value to be of type " + toString(valueTypeToExpressionType<T>()) +
-                    ", but found " + toString(typeOf(*upper)) + " instead."
-                };
-            }
-            return util::interpolate(lower->get<T>(), upper->get<T>(), t);
-        }
-    }
-};
+ParseResult createInterpolate(type::Type type,
+                              Interpolator interpolator,
+                              std::unique_ptr<Expression> input,
+                              std::map<double, std::unique_ptr<Expression>> stops,
+                              ParsingContext& ctx);
 
 } // namespace expression
 } // namespace style
diff --git a/include/mbgl/style/function/convert.hpp b/include/mbgl/style/function/convert.hpp
index b34071d219..e5a5808e1d 100644
--- a/include/mbgl/style/function/convert.hpp
+++ b/include/mbgl/style/function/convert.hpp
@@ -91,22 +91,6 @@ struct Convert {
         return std::make_unique<detail::ErrorExpression>(message);
     }
     
-    template <typename OutputType>
-    static ParseResult makeInterpolate(type::Type type,
-                                 std::unique_ptr<Expression> input,
-                                 std::map<double, std::unique_ptr<Expression>> convertedStops,
-                                 Interpolator interpolator)
-    {
-        ParseResult curve = ParseResult(std::make_unique<Interpolate<OutputType>>(
-            std::move(type),
-            std::move(interpolator),
-            std::move(input),
-            std::move(convertedStops)
-        ));
-        assert(curve);
-        return std::move(*curve);
-    }
-    
     template <typename Key>
     static ParseResult makeMatch(type::Type type,
                                  std::unique_ptr<Expression> input,
@@ -191,11 +175,12 @@ struct Convert {
     template <typename T>
     static std::unique_ptr<Expression> toExpression(const ExponentialStops<T>& stops)
     {
-        ParseResult e = makeInterpolate<typename ValueConverter<T>::ExpressionType>(
-                                         valueTypeToExpressionType<T>(),
-                                         makeZoom(),
-                                         convertStops(stops.stops),
-                                         ExponentialInterpolator(stops.base));
+        ParsingContext ctx;
+        ParseResult e = createInterpolate(valueTypeToExpressionType<T>(),
+                                          ExponentialInterpolator(stops.base),
+                                          makeZoom(),
+                                          convertStops(stops.stops),
+                                          ctx);
         assert(e);
         return std::move(*e);
     }
@@ -214,10 +199,12 @@ struct Convert {
     static std::unique_ptr<Expression> toExpression(const std::string& property,
                                                   const ExponentialStops<T>& stops)
     {
-        ParseResult e = makeInterpolate<typename ValueConverter<T>::ExpressionType>(valueTypeToExpressionType<T>(),
-                                                                     makeGet(type::Number, property),
-                                                                     convertStops(stops.stops),
-                                                                     ExponentialInterpolator(stops.base));
+        ParsingContext ctx;
+        ParseResult e = createInterpolate(valueTypeToExpressionType<T>(),
+                                          ExponentialInterpolator(stops.base),
+                                          makeGet(type::Number, property),
+                                          convertStops(stops.stops),
+                                          ctx);
         assert(e);
         return std::move(*e);
     }
@@ -247,10 +234,12 @@ struct Convert {
     template <typename T>
     static typename std::enable_if_t<util::Interpolatable<T>::value,
     ParseResult> makeZoomCurve(std::map<double, std::unique_ptr<Expression>> stops) {
-        return makeInterpolate<typename ValueConverter<T>::ExpressionType>(valueTypeToExpressionType<T>(),
-                                                                           makeZoom(),
-                                                                           std::move(stops),
-                                                                           ExponentialInterpolator(1.0));
+        ParsingContext ctx;
+        return createInterpolate(valueTypeToExpressionType<T>(),
+                                 ExponentialInterpolator(1.0),
+                                 makeZoom(),
+                                 std::move(stops),
+                                 ctx);
     }
     
     // non-interpolatable zoom curve
@@ -264,13 +253,15 @@ struct Convert {
     static std::unique_ptr<Expression> toExpression(const std::string& property,
                                                   const CompositeExponentialStops<T>& stops)
     {
+        ParsingContext ctx;
+
         std::map<double, std::unique_ptr<Expression>> outerStops;
         for (const std::pair<float, std::map<float, T>>& stop : stops.stops) {
-            std::unique_ptr<Expression> get = makeGet(type::Number, property);
-            ParseResult innerInterpolate = makeInterpolate<typename ValueConverter<T>::ExpressionType>(valueTypeToExpressionType<T>(),
-                                                                                  std::move(get),
-                                                                                  convertStops(stop.second),
-                                                                                  ExponentialInterpolator(stops.base));
+            ParseResult innerInterpolate = createInterpolate(valueTypeToExpressionType<T>(),
+                                                             ExponentialInterpolator(stops.base),
+                                                             makeGet(type::Number, property),
+                                                             convertStops(stop.second),
+                                                             ctx);
             assert(innerInterpolate);
             outerStops.emplace(stop.first, std::move(*innerInterpolate));
         }