1 files changed, 73 insertions, 0 deletions
diff --git a/src/mbgl/style/expression/assertion.cpp b/src/mbgl/style/expression/assertion.cpp
new file mode 100644
index 0000000000..a17c53cf54
--- /dev/null
+++ b/src/mbgl/style/expression/assertion.cpp
@@ -0,0 +1,73 @@
+#include <mbgl/style/expression/assertion.hpp>
+#include <mbgl/style/expression/check_subtype.hpp>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+using namespace mbgl::style::conversion;
+ParseResult Assertion::parse(const Convertible& value, ParsingContext& ctx) {
+    static std::unordered_map<std::string, type::Type> types {
+        {"string", type::String},
+        {"number", type::Number},
+        {"boolean", type::Boolean},
+        {"object", type::Object}
+    };
+
+    std::size_t length = arrayLength(value);
+
+    if (length < 2) {
+        ctx.error("Expected at least one argument.");
+        return ParseResult();
+    }
+
+    auto it = types.find(*toString(arrayMember(value, 0)));
+    assert(it != types.end());
+    
+    std::vector<std::unique_ptr<Expression>> parsed;
+    parsed.reserve(length - 1);
+    for (std::size_t i = 1; i < length; i++) {
+        ParseResult input = ctx.parse(arrayMember(value, i), i, {type::Value});
+        if (!input) return ParseResult();
+        parsed.push_back(std::move(*input));
+    }
+
+    return ParseResult(std::make_unique<Assertion>(it->second, std::move(parsed)));
+}
+
+EvaluationResult Assertion::evaluate(const EvaluationContext& params) const {
+    for (std::size_t i = 0; i < inputs.size(); i++) {
+        EvaluationResult value = inputs[i]->evaluate(params);
+        if (!value) return value;
+        if (!type::checkSubtype(getType(), typeOf(*value))) {
+            return value;
+        } else if (i == inputs.size() - 1) {
+            return EvaluationError {
+                "Expected value to be of type " + toString(getType()) +
+                ", but found " + toString(typeOf(*value)) + " instead."
+            };
+        }
+    }
+
+    assert(false);
+    return EvaluationError { "Unreachable" };
+};
+
+void Assertion::eachChild(const std::function<void(const Expression&)>& visit) const {
+    for(const std::unique_ptr<Expression>& input : inputs) {
+        visit(*input);
+    }
+};
+
+bool Assertion::operator==(const Expression& e) const {
+    if (auto rhs = dynamic_cast<const Assertion*>(&e)) {
+        return getType() == rhs->getType() && Expression::childrenEqual(inputs, rhs->inputs);
+    }
+    return false;
+}
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl
+
+