[core] Auto-convert concat arguments to strings

3 files changed, 15 insertions, 9 deletions

diff --git a/include/mbgl/style/expression/value.hpp b/include/mbgl/style/expression/value.hpp
index b1126118a9..2036ab8abe 100644
--- a/include/mbgl/style/expression/value.hpp
+++ b/include/mbgl/style/expression/value.hpp
@@ -46,6 +46,8 @@ struct Value : ValueBase {
 constexpr NullValue Null = NullValue();
 
 type::Type typeOf(const Value& value);
+
+std::string toString(const Value& value);
 std::string stringify(const Value& value);
 
 /*
diff --git a/src/mbgl/style/expression/compound_expression.cpp b/src/mbgl/style/expression/compound_expression.cpp
index 6e87167d5a..f5cbd7030b 100644
--- a/src/mbgl/style/expression/compound_expression.cpp
+++ b/src/mbgl/style/expression/compound_expression.cpp
@@ -310,12 +310,7 @@ std::unordered_map<std::string, CompoundExpressionRegistry::Definition> initiali
     define("typeof", [](const Value& v) -> Result<std::string> { return toString(typeOf(v)); });
 
     define("to-string", [](const Value& value) -> Result<std::string> {
-        return value.match(
-            [](const NullValue&) -> Result<std::string> { return std::string(); },
-            [](const Color& c) -> Result<std::string> { return c.stringify(); }, // avoid quoting
-            [](const std::string& s) -> Result<std::string> { return s; }, // avoid quoting
-            [](const auto& v) -> Result<std::string> { return stringify(v); }
-        );
+        return toString(value);
     });
 
     define("to-boolean", [](const Value& v) -> Result<bool> {
@@ -507,10 +502,10 @@ std::unordered_map<std::string, CompoundExpressionRegistry::Definition> initiali
     define("downcase", [](const std::string& input) -> Result<std::string> {
         return platform::lowercase(input);
     });
-    define("concat", [](const Varargs<std::string>& args) -> Result<std::string> {
+    define("concat", [](const Varargs<Value>& args) -> Result<std::string> {
         std::string s;
-        for (const std::string& arg : args) {
-            s += arg;
+        for (const Value& arg : args) {
+            s += toString(arg);
         }
         return s;
     });
diff --git a/src/mbgl/style/expression/value.cpp b/src/mbgl/style/expression/value.cpp
index f089c918cd..4bac8116c2 100644
--- a/src/mbgl/style/expression/value.cpp
+++ b/src/mbgl/style/expression/value.cpp
@@ -34,6 +34,15 @@ type::Type typeOf(const Value& value) {
     );
 }
 
+std::string toString(const Value& value) {
+    return value.match(
+        [](const NullValue&) { return std::string(); },
+        [](const Color& c) { return c.stringify(); }, // avoid quoting
+        [](const std::string& s) { return s; }, // avoid quoting
+        [](const auto& v_) { return stringify(v_); }
+    );
+}
+
 void writeJSON(rapidjson::Writer<rapidjson::StringBuffer>& writer, const Value& value) {
     value.match(
         [&] (const NullValue&) { writer.Null(); },