[core] Replace expressions RTTI with enums + static cast

15 files changed, 68 insertions, 27 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_))