1 files changed, 83 insertions, 0 deletions
diff --git a/src/mbgl/style/expression/equals.cpp b/src/mbgl/style/expression/equals.cpp
new file mode 100644
index 0000000000..08ef85e92b
--- /dev/null
+++ b/src/mbgl/style/expression/equals.cpp
@@ -0,0 +1,83 @@
+#include <mbgl/style/expression/equals.hpp>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+Equals::Equals(std::unique_ptr<Expression> lhs_, std::unique_ptr<Expression> rhs_, bool negate_)
+    : Expression(type::Boolean),
+      lhs(std::move(lhs_)),
+      rhs(std::move(rhs_)),
+      negate(negate_) {
+}
+
+EvaluationResult Equals::evaluate(const EvaluationContext& params) const {
+    EvaluationResult lhsResult = lhs->evaluate(params);
+    if (!lhsResult) return lhsResult;
+
+    EvaluationResult rhsResult = rhs->evaluate(params);
+    if (!rhsResult) return lhsResult;
+
+    bool result = *lhsResult == *rhsResult;
+    if (negate) {
+        result = !result;
+    }
+    return result;
+}
+
+void Equals::eachChild(const std::function<void(const Expression&)>& visit) const {
+    visit(*lhs);
+    visit(*rhs);
+}
+
+bool Equals::operator==(const Expression& e) const {
+    if (auto eq = dynamic_cast<const Equals*>(&e)) {
+        return eq->negate == negate && *eq->lhs == *lhs && *eq->rhs == *rhs;
+    }
+    return false;
+}
+
+static bool isComparableType(const type::Type& type) {
+    return type == type::String ||
+        type == type::Number ||
+        type == type::Boolean ||
+        type == type::Null;
+}
+
+using namespace mbgl::style::conversion;
+ParseResult Equals::parse(const Convertible& value, ParsingContext& ctx) {
+    std::size_t length = arrayLength(value);
+
+    if (length != 3) {
+        ctx.error("Expected two arguments.");
+        return ParseResult();
+    }
+
+    bool negate = toString(arrayMember(value, 0)) == std::string("!=");
+
+    ParseResult lhs = ctx.parse(arrayMember(value, 1), 1, {type::Value});
+    if (!lhs) return ParseResult();
+
+    ParseResult rhs = ctx.parse(arrayMember(value, 2), 2, {type::Value});
+    if (!rhs) return ParseResult();
+
+    type::Type lhsType = (*lhs)->getType();
+    type::Type rhsType = (*rhs)->getType();
+
+    if (!isComparableType(lhsType) && !isComparableType(rhsType)) {
+        ctx.error("Expected at least one argument to be a string, number, boolean, or null, but found (" +
+            toString(lhsType) + ", " + toString(rhsType) + ") instead.");
+        return ParseResult();
+    }
+
+    if (lhsType != rhsType && lhsType != type::Value && rhsType != type::Value) {
+        ctx.error("Cannot compare " + toString(lhsType) + " and " + toString(rhsType) + ".");
+        return ParseResult();
+    }
+
+    return ParseResult(std::make_unique<Equals>(std::move(*lhs), std::move(*rhs), negate));
+}
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl