3 files changed, 40 insertions, 0 deletions
diff --git a/include/mbgl/util/enum.hpp b/include/mbgl/util/enum.hpp
index 369ca86bfd..608befd3c4 100644
--- a/include/mbgl/util/enum.hpp
+++ b/include/mbgl/util/enum.hpp
@@ -11,6 +11,7 @@ namespace mbgl {
 template <typename T>
 class Enum {
 public:
+    using Type = T;
     static const char * toString(T);
     static optional<T> toEnum(const std::string&);
 };
diff --git a/include/mbgl/util/interpolate.hpp b/include/mbgl/util/interpolate.hpp
index 6738987598..aff730a0a2 100644
--- a/include/mbgl/util/interpolate.hpp
+++ b/include/mbgl/util/interpolate.hpp
@@ -3,6 +3,7 @@
 #include <mbgl/util/color.hpp>
 #include <mbgl/util/range.hpp>
 #include <mbgl/style/position.hpp>
+#include <mbgl/style/expression/value.hpp>
 
 #include <array>
 #include <vector>
@@ -47,6 +48,36 @@ public:
     }
 };
 
+
+// In order to accept Array<Number, N> as an output value for Curve
+// expressions, we need to have an interpolatable std::vector type.
+// However, style properties like line-dasharray are represented using
+// std::vector<float>, and should NOT be considered interpolatable.
+// So, we use std::vector<Value> to represent expression array values,
+// asserting that (a) the vectors are the same size, and (b) they contain
+// only numeric values.  (These invariants should be relatively safe,
+// being enforced by the expression type system.)
+template<>
+struct Interpolator<std::vector<style::expression::Value>> {
+    std::vector<style::expression::Value> operator()(const std::vector<style::expression::Value>& a,
+                                  const std::vector<style::expression::Value>& b,
+                                  const double t) const {
+        assert(a.size() == b.size());
+        if (a.size() == 0) return {};
+        std::vector<style::expression::Value> result;
+        for (std::size_t i = 0; i < a.size(); i++) {
+            assert(a[i].template is<double>());
+            assert(b[i].template is<double>());
+            style::expression::Value item = interpolate(
+                a[i].template get<double>(),
+                b[i].template get<double>(),
+                t);
+            result.push_back(item);
+        }
+        return result;
+    }
+};
+
 template <>
 struct Interpolator<style::Position> {
 public:
@@ -101,5 +132,7 @@ struct Interpolatable
       std::true_type,
       std::false_type> {};
 
+
+
 } // namespace util
 } // namespace mbgl
diff --git a/include/mbgl/util/unitbezier.hpp b/include/mbgl/util/unitbezier.hpp
index 6e644e2d1f..92f23d6718 100644
--- a/include/mbgl/util/unitbezier.hpp
+++ b/include/mbgl/util/unitbezier.hpp
@@ -26,6 +26,7 @@
 #pragma once
 
 #include <cmath>
+#include <tuple>
 
 namespace mbgl {
 namespace util {
@@ -102,6 +103,11 @@ struct UnitBezier {
     double solve(double x, double epsilon) const {
         return sampleCurveY(solveCurveX(x, epsilon));
     }
+    
+    bool operator==(const UnitBezier& rhs) const {
+        return std::tie(cx, bx, ax, cy, by, ay) ==
+            std::tie(rhs.cx, rhs.bx, rhs.ax, rhs.cy, rhs.by, rhs.ay);
+    }
 
 private:
     const double cx;