[core] Fix GCC8's new -Wcatch-value warnings

Polymorphic types shouldn't be caught by value, as the warning message says. Catch them by constant reference instead.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/mbgl/style/expression/coercion.cpp b/src/mbgl/style/expression/coercion.cpp
index d9cd3ffdc9..0166d144e0 100644
--- a/src/mbgl/style/expression/coercion.cpp
+++ b/src/mbgl/style/expression/coercion.cpp
@@ -13,7 +13,7 @@ EvaluationResult toNumber(const Value& v) {
         [](const std::string& s) -> optional<double> {
             try {
                 return util::stof(s);
-            } catch(std::exception) {
+            } catch (const std::exception&) {
                 return optional<double>();
             }
         },