From d13ebedadbd6ef9d6308c3399d0d88b140de421d Mon Sep 17 00:00:00 2001
From: Bruno de Oliveira Abinader <bruno@mapbox.com>
Date: Fri, 20 Jul 2018 15:40:47 +0300
Subject: [core] Replace expressions RTTI with enums + static cast

---
 .../conversion/data_driven_property_value.hpp      |  8 +++--
 include/mbgl/style/conversion/property_value.hpp   |  8 +++--
 include/mbgl/style/expression/array_assertion.hpp  |  5 +--
 include/mbgl/style/expression/at.hpp               |  5 +--
 include/mbgl/style/expression/boolean_operator.hpp |  4 +--
 include/mbgl/style/expression/case.hpp             |  2 +-
 include/mbgl/style/expression/coalesce.hpp         |  2 +-
 .../mbgl/style/expression/compound_expression.hpp  |  5 +--
 include/mbgl/style/expression/error.hpp            |  4 +--
 include/mbgl/style/expression/expression.hpp       | 27 ++++++++++++++-
 include/mbgl/style/expression/interpolate.hpp      |  3 +-
 include/mbgl/style/expression/is_constant.hpp      |  3 +-
 include/mbgl/style/expression/let.hpp              | 10 +++---
 include/mbgl/style/expression/literal.hpp          |  7 ++--
 include/mbgl/style/expression/match.hpp            |  2 +-
 src/mbgl/style/expression/assertion.cpp            |  5 +--
 src/mbgl/style/expression/boolean_operator.cpp     |  6 ++--
 src/mbgl/style/expression/case.cpp                 |  3 +-
 src/mbgl/style/expression/coalesce.cpp             |  3 +-
 src/mbgl/style/expression/coercion.cpp             |  5 +--
 src/mbgl/style/expression/collator_expression.cpp  |  5 +--
 src/mbgl/style/expression/equals.cpp               |  5 +--
 src/mbgl/style/expression/find_zoom_curve.cpp      | 39 ++++++++++++++++------
 src/mbgl/style/expression/interpolate.cpp          |  2 +-
 src/mbgl/style/expression/is_constant.cpp          |  5 +--
 src/mbgl/style/expression/length.cpp               |  5 +--
 src/mbgl/style/expression/match.cpp                |  3 +-
 src/mbgl/style/expression/parsing_context.cpp      | 16 +++++----
 src/mbgl/style/expression/step.cpp                 |  5 +--
 29 files changed, 138 insertions(+), 64 deletions(-)

diff --git a/include/mbgl/style/conversion/data_driven_property_value.hpp b/include/mbgl/style/conversion/data_driven_property_value.hpp
index f1bd1bdbb7..59d197b216 100644
--- a/include/mbgl/style/conversion/data_driven_property_value.hpp
+++ b/include/mbgl/style/conversion/data_driven_property_value.hpp
@@ -47,13 +47,17 @@ struct Converter<DataDrivenPropertyValue<T>> {
             return {};
         } else if (!(*expression).isFeatureConstant() || !(*expression).isZoomConstant()) {
             return { std::move(*expression) };
-        } else {
+        } else if ((*expression).getExpression().getKind() == Kind::Literal) {
             optional<T> constant = fromExpressionValue<T>(
-                dynamic_cast<const Literal&>((*expression).getExpression()).getValue());
+                static_cast<const Literal&>((*expression).getExpression()).getValue());
             if (!constant) {
                 return {};
             }
             return DataDrivenPropertyValue<T>(*constant);
+        } else {
+            assert(false);
+            error = { "expected a literal expression" };
+            return {};
         }
     }
 
diff --git a/include/mbgl/style/conversion/property_value.hpp b/include/mbgl/style/conversion/property_value.hpp
index db23074c5e..b03655a848 100644
--- a/include/mbgl/style/conversion/property_value.hpp
+++ b/include/mbgl/style/conversion/property_value.hpp
@@ -54,13 +54,17 @@ struct Converter<PropertyValue<T>> {
             return {};
         } else if (!(*expression).isZoomConstant()) {
             return { std::move(*expression) };
-        } else {
+        } else if ((*expression).getExpression().getKind() == Kind::Literal) {
             optional<T> constant = fromExpressionValue<T>(
-                dynamic_cast<const Literal&>((*expression).getExpression()).getValue());
+                static_cast<const Literal&>((*expression).getExpression()).getValue());
             if (!constant) {
                 return {};
             }
             return PropertyValue<T>(*constant);
+        } else {
+            assert(false);
+            error = { "expected a literal expression" };
+            return {};
         }
     }
 };
diff --git a/include/mbgl/style/expression/array_assertion.hpp b/include/mbgl/style/expression/array_assertion.hpp
index af153611ff..0c0912b73e 100644
--- a/include/mbgl/style/expression/array_assertion.hpp
+++ b/include/mbgl/style/expression/array_assertion.hpp
@@ -14,7 +14,7 @@ namespace expression {
 class ArrayAssertion : public Expression  {
 public:
     ArrayAssertion(type::Array type_, std::unique_ptr<Expression> input_) :
-        Expression(type_),
+        Expression(Kind::ArrayAssertion, type_),
         input(std::move(input_))
     {}
 
@@ -24,7 +24,8 @@ public:
     void eachChild(const std::function<void(const Expression&)>& visit) const override;
 
     bool operator==(const Expression& e) const override {
-        if (auto rhs = dynamic_cast<const ArrayAssertion*>(&e)) {
+        if (e.getKind() == Kind::ArrayAssertion) {
+            auto rhs = static_cast<const ArrayAssertion*>(&e);
             return getType() == rhs->getType() && *input == *(rhs->input);
         }
         return false;
diff --git a/include/mbgl/style/expression/at.hpp b/include/mbgl/style/expression/at.hpp
index 1e6f1c7dd2..f0dbccb794 100644
--- a/include/mbgl/style/expression/at.hpp
+++ b/include/mbgl/style/expression/at.hpp
@@ -11,7 +11,7 @@ namespace expression {
 class At : public Expression {
 public:
     At(std::unique_ptr<Expression> index_, std::unique_ptr<Expression> input_) :
-        Expression(input_->getType().get<type::Array>().itemType),
+        Expression(Kind::At, input_->getType().get<type::Array>().itemType),
         index(std::move(index_)),
         input(std::move(input_))
     {}
@@ -22,7 +22,8 @@ public:
     void eachChild(const std::function<void(const Expression&)>&) const override;
 
     bool operator==(const Expression& e) const override {
-        if (auto rhs = dynamic_cast<const At*>(&e)) {
+        if (e.getKind() == Kind::At) {
+            auto rhs = static_cast<const At*>(&e);
             return *index == *(rhs->index) && *input == *(rhs->input);
         }
         return false;
diff --git a/include/mbgl/style/expression/boolean_operator.hpp b/include/mbgl/style/expression/boolean_operator.hpp
index 6d0f85756a..d254747513 100644
--- a/include/mbgl/style/expression/boolean_operator.hpp
+++ b/include/mbgl/style/expression/boolean_operator.hpp
@@ -12,7 +12,7 @@ namespace expression {
 class Any : public Expression  {
 public:
     Any(std::vector<std::unique_ptr<Expression>> inputs_) :
-        Expression(type::Boolean),
+        Expression(Kind::Any, type::Boolean),
         inputs(std::move(inputs_))
     {}
 
@@ -31,7 +31,7 @@ private:
 class All : public Expression  {
 public:
     All(std::vector<std::unique_ptr<Expression>> inputs_) :
-        Expression(type::Boolean),
+        Expression(Kind::All, type::Boolean),
         inputs(std::move(inputs_))
     {}
 
diff --git a/include/mbgl/style/expression/case.hpp b/include/mbgl/style/expression/case.hpp
index 667ca53712..02dc3bc4c2 100644
--- a/include/mbgl/style/expression/case.hpp
+++ b/include/mbgl/style/expression/case.hpp
@@ -16,7 +16,7 @@ public:
     using Branch = std::pair<std::unique_ptr<Expression>, std::unique_ptr<Expression>>;
 
     Case(type::Type type_, std::vector<Branch> branches_, std::unique_ptr<Expression> otherwise_)
-        : Expression(type_), branches(std::move(branches_)), otherwise(std::move(otherwise_)) {
+        : Expression(Kind::Case, type_), branches(std::move(branches_)), otherwise(std::move(otherwise_)) {
     }
 
     static ParseResult parse(const mbgl::style::conversion::Convertible& value, ParsingContext& ctx);
diff --git a/include/mbgl/style/expression/coalesce.hpp b/include/mbgl/style/expression/coalesce.hpp
index a858bef695..cd60cee02e 100644
--- a/include/mbgl/style/expression/coalesce.hpp
+++ b/include/mbgl/style/expression/coalesce.hpp
@@ -15,7 +15,7 @@ class Coalesce : public Expression {
 public:
     using Args = std::vector<std::unique_ptr<Expression>>;
     Coalesce(const type::Type& type_, Args args_) :
-        Expression(type_),
+        Expression(Kind::Coalesce, type_),
         args(std::move(args_))
     {}
 
diff --git a/include/mbgl/style/expression/compound_expression.hpp b/include/mbgl/style/expression/compound_expression.hpp
index 9d39194563..04562752a6 100644
--- a/include/mbgl/style/expression/compound_expression.hpp
+++ b/include/mbgl/style/expression/compound_expression.hpp
@@ -62,7 +62,7 @@ struct SignatureBase {
 class CompoundExpressionBase : public Expression {
 public:
     CompoundExpressionBase(std::string name_, const detail::SignatureBase& signature) :
-        Expression(signature.result),
+        Expression(Kind::CompoundExpression, signature.result),
         name(std::move(name_)),
         params(signature.params)
     {}
@@ -108,7 +108,8 @@ public:
     }
 
     bool operator==(const Expression& e) const override {
-        if (auto rhs = dynamic_cast<const CompoundExpression*>(&e)) {
+        if (e.getKind() == Kind::CompoundExpression) {
+            auto rhs = static_cast<const CompoundExpression*>(&e);
             return getName() == rhs->getName() && Expression::childrenEqual(args, rhs->args);
         }
         return false;
diff --git a/include/mbgl/style/expression/error.hpp b/include/mbgl/style/expression/error.hpp
index bfb9247d11..9e1da2f0f0 100644
--- a/include/mbgl/style/expression/error.hpp
+++ b/include/mbgl/style/expression/error.hpp
@@ -11,13 +11,13 @@ namespace expression {
 class Error : public Expression {
 public:
     Error(std::string message_) 
-        : Expression(type::Error),
+        : Expression(Kind::Error, type::Error),
           message(std::move(message_)) {}
 
     void eachChild(const std::function<void(const Expression&)>&) const override {}
 
     bool operator==(const Expression& e) const override {
-        return dynamic_cast<const Error*>(&e);
+        return e.getKind() == Kind::Error;
     }
 
     EvaluationResult evaluate(const EvaluationContext&) const override {
diff --git a/include/mbgl/style/expression/expression.hpp b/include/mbgl/style/expression/expression.hpp
index c41ac0b5f1..8301f1572c 100644
--- a/include/mbgl/style/expression/expression.hpp
+++ b/include/mbgl/style/expression/expression.hpp
@@ -113,9 +113,32 @@ public:
     ParseResult ExpressionClass::parse(const V&, ParsingContext),
     which handles parsing a style-spec JSON representation of the expression.
 */
+
+enum class Kind : int32_t {
+    Coalesce,
+    CompoundExpression,
+    Literal,
+    ArrayAssertion,
+    At,
+    Interpolate,
+    Assertion,
+    Length,
+    Step,
+    Let,
+    Var,
+    CollatorExpression,
+    Coercion,
+    Match,
+    Error,
+    Case,
+    Any,
+    All,
+    Equals,
+};
+
 class Expression {
 public:
-    Expression(type::Type type_) : type(std::move(type_)) {}
+    Expression(Kind kind_, type::Type type_) : kind(kind_), type(std::move(type_)) {}
     virtual ~Expression() = default;
     
     virtual EvaluationResult evaluate(const EvaluationContext& params) const = 0;
@@ -125,6 +148,7 @@ public:
         return !operator==(rhs);
     }
 
+    Kind getKind() const { return kind; };
     type::Type getType() const { return type; };
     
     EvaluationResult evaluate(optional<float> zoom, const Feature& feature, optional<double> heatmapDensity) const;
@@ -182,6 +206,7 @@ protected:
     }
 
 private:
+    Kind kind;
     type::Type type;
 };
 
diff --git a/include/mbgl/style/expression/interpolate.hpp b/include/mbgl/style/expression/interpolate.hpp
index 0aca6909a3..0e78504719 100644
--- a/include/mbgl/style/expression/interpolate.hpp
+++ b/include/mbgl/style/expression/interpolate.hpp
@@ -51,7 +51,8 @@ public:
     }
 
     bool operator==(const Expression& e) const override {
-        if (auto rhs = dynamic_cast<const Interpolate*>(&e)) {
+        if (e.getKind() == Kind::Interpolate) {
+            auto rhs = static_cast<const Interpolate*>(&e);
             if (interpolator != rhs->interpolator ||
                 *input != *(rhs->input) ||
                 stops.size() != rhs->stops.size())
diff --git a/include/mbgl/style/expression/is_constant.hpp b/include/mbgl/style/expression/is_constant.hpp
index 29e03ccbc0..065fa30db1 100644
--- a/include/mbgl/style/expression/is_constant.hpp
+++ b/include/mbgl/style/expression/is_constant.hpp
@@ -9,7 +9,8 @@ namespace expression {
 
 template <typename T>
 bool isGlobalPropertyConstant(const Expression& expression, const T& properties) {
-    if (auto e = dynamic_cast<const CompoundExpressionBase*>(&expression)) {
+    if (expression.getKind() == Kind::CompoundExpression) {
+        auto e = static_cast<const CompoundExpressionBase*>(&expression);
         for (const std::string& property : properties) {
             if (e->getName() == property) {
                 return false;
diff --git a/include/mbgl/style/expression/let.hpp b/include/mbgl/style/expression/let.hpp
index d0210d8bba..d11ba1b976 100644
--- a/include/mbgl/style/expression/let.hpp
+++ b/include/mbgl/style/expression/let.hpp
@@ -16,7 +16,7 @@ public:
     using Bindings = std::map<std::string, std::shared_ptr<Expression>>;
     
     Let(Bindings bindings_, std::unique_ptr<Expression> result_) :
-        Expression(result_->getType()),
+        Expression(Kind::Let, result_->getType()),
         bindings(std::move(bindings_)),
         result(std::move(result_))
     {}
@@ -27,7 +27,8 @@ public:
     void eachChild(const std::function<void(const Expression&)>&) const override;
 
     bool operator==(const Expression& e) const override {
-        if (auto rhs = dynamic_cast<const Let*>(&e)) {
+        if (e.getKind() == Kind::Let) {
+            auto rhs = static_cast<const Let*>(&e);
             return *result == *(rhs->result);
         }
         return false;
@@ -49,7 +50,7 @@ private:
 class Var : public Expression {
 public:
     Var(std::string name_, std::shared_ptr<Expression> value_) :
-        Expression(value_->getType()),
+        Expression(Kind::Var, value_->getType()),
         name(std::move(name_)),
         value(value_)
     {}
@@ -60,7 +61,8 @@ public:
     void eachChild(const std::function<void(const Expression&)>&) const override;
 
     bool operator==(const Expression& e) const override {
-        if (auto rhs = dynamic_cast<const Var*>(&e)) {
+        if (e.getKind() == Kind::Var) {
+            auto rhs = static_cast<const Var*>(&e);
             return *value == *(rhs->value);
         }
         return false;
diff --git a/include/mbgl/style/expression/literal.hpp b/include/mbgl/style/expression/literal.hpp
index 44c095bf28..bcae23b1fa 100644
--- a/include/mbgl/style/expression/literal.hpp
+++ b/include/mbgl/style/expression/literal.hpp
@@ -13,12 +13,12 @@ namespace expression {
 class Literal : public Expression {
 public:
     Literal(Value value_)
-        : Expression(typeOf(value_))
+        : Expression(Kind::Literal, typeOf(value_))
         , value(value_)
     {}
     
     Literal(type::Array type_, std::vector<Value> value_)
-        : Expression(type_)
+        : Expression(Kind::Literal, type_)
         , value(value_)
     {}
 
@@ -31,7 +31,8 @@ public:
     void eachChild(const std::function<void(const Expression&)>&) const override {}
     
     bool operator==(const Expression& e) const override {
-        if (auto rhs = dynamic_cast<const Literal*>(&e)) {
+        if (e.getKind() == Kind::Literal) {
+            auto rhs = static_cast<const Literal*>(&e);
             return value == rhs->value;
         }
         return false;
diff --git a/include/mbgl/style/expression/match.hpp b/include/mbgl/style/expression/match.hpp
index 3775e38067..2ce4b7a533 100644
--- a/include/mbgl/style/expression/match.hpp
+++ b/include/mbgl/style/expression/match.hpp
@@ -19,7 +19,7 @@ public:
           std::unique_ptr<Expression> input_,
           Branches branches_,
           std::unique_ptr<Expression> otherwise_
-    ) : Expression(type_),
+    ) : Expression(Kind::Match, type_),
         input(std::move(input_)),
         branches(std::move(branches_)),
         otherwise(std::move(otherwise_))
diff --git a/src/mbgl/style/expression/assertion.cpp b/src/mbgl/style/expression/assertion.cpp
index eefc9e24f8..2434d7a2f8 100644
--- a/src/mbgl/style/expression/assertion.cpp
+++ b/src/mbgl/style/expression/assertion.cpp
@@ -8,7 +8,7 @@ namespace expression {
 using namespace mbgl::style::conversion;
 
 Assertion::Assertion(type::Type type_, std::vector<std::unique_ptr<Expression>> inputs_) :
-    Expression(type_),
+    Expression(Kind::Assertion, type_),
     inputs(std::move(inputs_))
 {
     assert(!inputs.empty());
@@ -72,7 +72,8 @@ void Assertion::eachChild(const std::function<void(const Expression&)>& visit) c
 };
 
 bool Assertion::operator==(const Expression& e) const {
-    if (auto rhs = dynamic_cast<const Assertion*>(&e)) {
+    if (e.getKind() == Kind::Assertion) {
+        auto rhs = static_cast<const Assertion*>(&e);
         return getType() == rhs->getType() && Expression::childrenEqual(inputs, rhs->inputs);
     }
     return false;
diff --git a/src/mbgl/style/expression/boolean_operator.cpp b/src/mbgl/style/expression/boolean_operator.cpp
index 8d277450ba..68e96129aa 100644
--- a/src/mbgl/style/expression/boolean_operator.cpp
+++ b/src/mbgl/style/expression/boolean_operator.cpp
@@ -20,7 +20,8 @@ void Any::eachChild(const std::function<void(const Expression&)>& visit) const {
 }
 
 bool Any::operator==(const Expression& e) const {
-    if (auto rhs = dynamic_cast<const Any*>(&e)) {
+    if (e.getKind() == Kind::Any) {
+        auto rhs = static_cast<const Any*>(&e);
         return Expression::childrenEqual(inputs, rhs->inputs);
     }
     return false;
@@ -47,7 +48,8 @@ void All::eachChild(const std::function<void(const Expression&)>& visit) const {
 }
 
 bool All::operator==(const Expression& e) const {
-    if (auto rhs = dynamic_cast<const All*>(&e)) {
+    if (e.getKind() == Kind::All) {
+        auto rhs = static_cast<const All*>(&e);
         return Expression::childrenEqual(inputs, rhs->inputs);
     }
     return false;
diff --git a/src/mbgl/style/expression/case.cpp b/src/mbgl/style/expression/case.cpp
index 295e694189..e885c0ce6b 100644
--- a/src/mbgl/style/expression/case.cpp
+++ b/src/mbgl/style/expression/case.cpp
@@ -28,7 +28,8 @@ void Case::eachChild(const std::function<void(const Expression&)>& visit) const
 }
 
 bool Case::operator==(const Expression& e) const {
-    if (auto rhs = dynamic_cast<const Case*>(&e)) {
+    if (e.getKind() == Kind::Case) {
+        auto rhs = static_cast<const Case*>(&e);
         return *otherwise == *(rhs->otherwise) && Expression::childrenEqual(branches, rhs->branches);
     }
     return false;
diff --git a/src/mbgl/style/expression/coalesce.cpp b/src/mbgl/style/expression/coalesce.cpp
index 872a9abbef..0090f16009 100644
--- a/src/mbgl/style/expression/coalesce.cpp
+++ b/src/mbgl/style/expression/coalesce.cpp
@@ -21,7 +21,8 @@ void Coalesce::eachChild(const std::function<void(const Expression&)>& visit) co
 }
 
 bool Coalesce::operator==(const Expression& e) const {
-    if (auto rhs = dynamic_cast<const Coalesce*>(&e)) {
+    if (e.getKind() == Kind::Coalesce) {
+        auto rhs = static_cast<const Coalesce*>(&e);
         return Expression::childrenEqual(args, rhs->args);
     }
     return false;
diff --git a/src/mbgl/style/expression/coercion.cpp b/src/mbgl/style/expression/coercion.cpp
index 11172a3668..f5a4d70f66 100644
--- a/src/mbgl/style/expression/coercion.cpp
+++ b/src/mbgl/style/expression/coercion.cpp
@@ -68,7 +68,7 @@ EvaluationResult toColor(const Value& colorValue) {
 }
 
 Coercion::Coercion(type::Type type_, std::vector<std::unique_ptr<Expression>> inputs_) :
-    Expression(std::move(type_)),
+    Expression(Kind::Coercion, std::move(type_)),
     inputs(std::move(inputs_))
 {
     assert(!inputs.empty());
@@ -138,7 +138,8 @@ void Coercion::eachChild(const std::function<void(const Expression&)>& visit) co
 };
 
 bool Coercion::operator==(const Expression& e) const {
-    if (auto rhs = dynamic_cast<const Coercion*>(&e)) {
+    if (e.getKind() == Kind::Coercion) {
+        auto rhs = static_cast<const Coercion*>(&e);
         return getType() == rhs->getType() && Expression::childrenEqual(inputs, rhs->inputs);
     }
     return false;
diff --git a/src/mbgl/style/expression/collator_expression.cpp b/src/mbgl/style/expression/collator_expression.cpp
index f5e4e3fdff..b27eedbc76 100644
--- a/src/mbgl/style/expression/collator_expression.cpp
+++ b/src/mbgl/style/expression/collator_expression.cpp
@@ -10,7 +10,7 @@ namespace expression {
 CollatorExpression::CollatorExpression(std::unique_ptr<Expression> caseSensitive_,
                    std::unique_ptr<Expression> diacriticSensitive_,
                    optional<std::unique_ptr<Expression>> locale_)
-    : Expression(type::Collator)
+    : Expression(Kind::CollatorExpression, type::Collator)
     , caseSensitive(std::move(caseSensitive_))
     , diacriticSensitive(std::move(diacriticSensitive_))
     , locale(std::move(locale_))
@@ -73,7 +73,8 @@ void CollatorExpression::eachChild(const std::function<void(const Expression&)>&
 }
     
 bool CollatorExpression::operator==(const Expression& e) const {
-    if (auto rhs = dynamic_cast<const CollatorExpression*>(&e)) {
+    if (e.getKind() == Kind::CollatorExpression) {
+        auto rhs = static_cast<const CollatorExpression*>(&e);
         if ((locale && (!rhs->locale || **locale != **(rhs->locale))) ||
             (!locale && rhs->locale)) {
             return false;
diff --git a/src/mbgl/style/expression/equals.cpp b/src/mbgl/style/expression/equals.cpp
index 245899f975..73e2baf71b 100644
--- a/src/mbgl/style/expression/equals.cpp
+++ b/src/mbgl/style/expression/equals.cpp
@@ -13,7 +13,7 @@ static bool isComparableType(const type::Type& type) {
 }
 
 Equals::Equals(std::unique_ptr<Expression> lhs_, std::unique_ptr<Expression> rhs_, optional<std::unique_ptr<Expression>> collator_, bool negate_)
-    : Expression(type::Boolean),
+    : Expression(Kind::Equals, type::Boolean),
       lhs(std::move(lhs_)),
       rhs(std::move(rhs_)),
       collator(std::move(collator_)),
@@ -53,7 +53,8 @@ void Equals::eachChild(const std::function<void(const Expression&)>& visit) cons
 }
 
 bool Equals::operator==(const Expression& e) const {
-    if (auto eq = dynamic_cast<const Equals*>(&e)) {
+    if (e.getKind() == Kind::Equals) {
+        auto eq = static_cast<const Equals*>(&e);
         return eq->negate == negate && *eq->lhs == *lhs && *eq->rhs == *rhs;
     }
     return false;
diff --git a/src/mbgl/style/expression/find_zoom_curve.cpp b/src/mbgl/style/expression/find_zoom_curve.cpp
index 1e0a936605..a27f8560ef 100644
--- a/src/mbgl/style/expression/find_zoom_curve.cpp
+++ b/src/mbgl/style/expression/find_zoom_curve.cpp
@@ -14,9 +14,14 @@ namespace expression {
 optional<variant<const Interpolate*, const Step*, ParsingError>> findZoomCurve(const expression::Expression* e) {
     optional<variant<const Interpolate*, const Step*, ParsingError>> result;
     
-    if (auto let = dynamic_cast<const Let*>(e)) {
+    switch (e->getKind()) {
+    case Kind::Let: {
+        auto let = static_cast<const Let*>(e);
         result = findZoomCurve(let->getResult());
-    } else if (auto coalesce = dynamic_cast<const Coalesce*>(e)) {
+        break;
+    }
+    case Kind::Coalesce: {
+        auto coalesce = static_cast<const Coalesce*>(e);
         std::size_t length = coalesce->getLength();
         for (std::size_t i = 0; i < length; i++) {
             result = findZoomCurve(coalesce->getChild(i));
@@ -24,16 +29,30 @@ optional<variant<const Interpolate*, const Step*, ParsingError>> findZoomCurve(c
                 break;
             }
         }
-    } else if (auto curve = dynamic_cast<const Interpolate*>(e)) {
-        auto z = dynamic_cast<CompoundExpressionBase*>(curve->getInput().get());
-        if (z && z->getName() == "zoom") {
-            result = {curve};
+        break;
+    }
+    case Kind::Interpolate: {
+        auto curve = static_cast<const Interpolate*>(e);
+        if (curve->getInput()->getKind() == Kind::CompoundExpression) {
+            auto z = static_cast<CompoundExpressionBase*>(curve->getInput().get());
+            if (z && z->getName() == "zoom") {
+                result = {curve};
+            }
         }
-    } else if (auto step = dynamic_cast<const Step*>(e)) {
-        auto z = dynamic_cast<CompoundExpressionBase*>(step->getInput().get());
-        if (z && z->getName() == "zoom") {
-            result = {step};
+        break;
+    }
+    case Kind::Step: {
+        auto step = static_cast<const Step*>(e);
+        if (step->getInput()->getKind() == Kind::CompoundExpression) {
+            auto z = static_cast<CompoundExpressionBase*>(step->getInput().get());
+            if (z && z->getName() == "zoom") {
+                result = {step};
+            }
         }
+        break;
+    }
+    default:
+        break;
     }
     
     if (result && result->is<ParsingError>()) {
diff --git a/src/mbgl/style/expression/interpolate.cpp b/src/mbgl/style/expression/interpolate.cpp
index a9bb3bf05e..852042382c 100644
--- a/src/mbgl/style/expression/interpolate.cpp
+++ b/src/mbgl/style/expression/interpolate.cpp
@@ -264,7 +264,7 @@ Interpolate::Interpolate(const type::Type& type_,
                          Interpolator interpolator_,
                          std::unique_ptr<Expression> input_,
                          std::map<double, std::unique_ptr<Expression>> stops_)
-  : Expression(type_),
+  : Expression(Kind::Interpolate, type_),
     interpolator(std::move(interpolator_)),
     input(std::move(input_)),
     stops(std::move(stops_)) {
diff --git a/src/mbgl/style/expression/is_constant.cpp b/src/mbgl/style/expression/is_constant.cpp
index b877ed550a..3b1f1aba8c 100644
--- a/src/mbgl/style/expression/is_constant.cpp
+++ b/src/mbgl/style/expression/is_constant.cpp
@@ -9,7 +9,8 @@ namespace expression {
 constexpr static const char filter[] = "filter-";
 
 bool isFeatureConstant(const Expression& expression) {
-    if (auto e = dynamic_cast<const CompoundExpressionBase*>(&expression)) {
+    if (expression.getKind() == Kind::CompoundExpression) {
+        auto e = static_cast<const CompoundExpressionBase*>(&expression);
         const std::string name = e->getName();
         optional<std::size_t> parameterCount = e->getParameterCount();
         if (name == "get" && parameterCount && *parameterCount == 1) {
@@ -28,7 +29,7 @@ bool isFeatureConstant(const Expression& expression) {
         }
     }
     
-    if (dynamic_cast<const CollatorExpression*>(&expression)) {
+    if (expression.getKind() == Kind::CollatorExpression) {
         // Although the results of a Collator expression with fixed arguments
         // generally shouldn't change between executions, we can't serialize them
         // as constant expressions because results change based on environment.
diff --git a/src/mbgl/style/expression/length.cpp b/src/mbgl/style/expression/length.cpp
index 258353ae4e..ad7a15675a 100644
--- a/src/mbgl/style/expression/length.cpp
+++ b/src/mbgl/style/expression/length.cpp
@@ -6,7 +6,7 @@ namespace style {
 namespace expression {
 
 Length::Length(std::unique_ptr<Expression> input_)
-    : Expression(type::Number),
+    : Expression(Kind::Length, type::Number),
       input(std::move(input_)) {
 }
 
@@ -30,7 +30,8 @@ void Length::eachChild(const std::function<void(const Expression&)>& visit) cons
 }
 
 bool Length::operator==(const Expression& e) const {
-    if (auto eq = dynamic_cast<const Length*>(&e)) {
+    if (e.getKind() == Kind::Length) {
+        auto eq = static_cast<const Length*>(&e);
         return *eq->input == *input;
     }
     return false;
diff --git a/src/mbgl/style/expression/match.cpp b/src/mbgl/style/expression/match.cpp
index 59123c9812..340f1dab4d 100644
--- a/src/mbgl/style/expression/match.cpp
+++ b/src/mbgl/style/expression/match.cpp
@@ -18,7 +18,8 @@ void Match<T>::eachChild(const std::function<void(const Expression&)>& visit) co
 
 template <typename T>
 bool Match<T>::operator==(const Expression& e) const {
-    if (auto rhs = dynamic_cast<const Match*>(&e)) {
+    if (e.getKind() == Kind::Match) {
+        auto rhs = static_cast<const Match*>(&e);
         return (*input == *(rhs->input) &&
                 *otherwise == *(rhs->otherwise) &&
                 Expression::childrenEqual(branches, rhs->branches));
diff --git a/src/mbgl/style/expression/parsing_context.cpp b/src/mbgl/style/expression/parsing_context.cpp
index fe3102f158..a4c04b03b1 100644
--- a/src/mbgl/style/expression/parsing_context.cpp
+++ b/src/mbgl/style/expression/parsing_context.cpp
@@ -32,19 +32,21 @@ namespace style {
 namespace expression {
 
 bool isConstant(const Expression& expression) {
-    if (auto varExpression = dynamic_cast<const Var*>(&expression)) {
+    if (expression.getKind() == Kind::Var) {
+        auto varExpression = static_cast<const Var*>(&expression);
         return isConstant(*varExpression->getBoundExpression());
     }
 
-    if (auto compound = dynamic_cast<const CompoundExpressionBase*>(&expression)) {
+    if (expression.getKind() == Kind::CompoundExpression) {
+        auto compound = static_cast<const CompoundExpressionBase*>(&expression);
         if (compound->getName() == "error") {
             return false;
         }
     }
 
-    bool isTypeAnnotation = dynamic_cast<const Coercion*>(&expression) ||
-        dynamic_cast<const Assertion*>(&expression) ||
-        dynamic_cast<const ArrayAssertion*>(&expression);
+    bool isTypeAnnotation = expression.getKind() == Kind::Coercion ||
+        expression.getKind() == Kind::Assertion ||
+        expression.getKind() == Kind::ArrayAssertion;
     
     bool childrenConstant = true;
     expression.eachChild([&](const Expression& child) {
@@ -58,7 +60,7 @@ bool isConstant(const Expression& expression) {
         if (isTypeAnnotation) {
             childrenConstant = childrenConstant && isConstant(child);
         } else {
-            childrenConstant = childrenConstant && dynamic_cast<const Literal*>(&child);
+            childrenConstant = childrenConstant && child.getKind() == Kind::Literal;
         }
     });
     if (!childrenConstant) {
@@ -186,7 +188,7 @@ ParseResult ParsingContext::parse(const Convertible& value, TypeAnnotationOption
     // If an expression's arguments are all constant, we can evaluate
     // it immediately and replace it with a literal value in the
     // parsed result.
-    if (!dynamic_cast<Literal *>(parsed->get()) && isConstant(**parsed)) {
+    if ((*parsed)->getKind() != Kind::Literal && isConstant(**parsed)) {
         EvaluationContext params(nullptr);
         EvaluationResult evaluated((*parsed)->evaluate(params));
         if (!evaluated) {
diff --git a/src/mbgl/style/expression/step.cpp b/src/mbgl/style/expression/step.cpp
index f42a2721a9..ee6055091e 100644
--- a/src/mbgl/style/expression/step.cpp
+++ b/src/mbgl/style/expression/step.cpp
@@ -11,7 +11,7 @@ namespace expression {
 Step::Step(const type::Type& type_,
            std::unique_ptr<Expression> input_,
            std::map<double, std::unique_ptr<Expression>> stops_)
-  : Expression(type_),
+  : Expression(Kind::Step, type_),
     input(std::move(input_)),
     stops(std::move(stops_))
 {
@@ -57,7 +57,8 @@ void Step::eachStop(const std::function<void(double, const Expression&)>& visit)
 }
 
 bool Step::operator==(const Expression& e) const {
-    if (auto rhs = dynamic_cast<const Step*>(&e)) {
+    if (e.getKind() == Kind::Step) {
+        auto rhs = static_cast<const Step*>(&e);
         return *input == *(rhs->input) && Expression::childrenEqual(stops, rhs->stops);
     }
     return false;
-- 
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