Consolidate `style::Layer` properties API

The `style::Layer` class now exposes all the properties contained at `style::LayerImpl`.
This allowed to drop `style::Layer::accept()` method usage, avoid the repeated generated code
and thus save some binary size.

This patch is a part of the layers modularization effort.

1 files changed, 6 insertions, 0 deletions

diff --git a/include/mbgl/util/immutable.hpp b/include/mbgl/util/immutable.hpp
index eb26c0d282..b4117166dd 100644
--- a/include/mbgl/util/immutable.hpp
+++ b/include/mbgl/util/immutable.hpp
@@ -39,6 +39,7 @@ private:
 
     template <class S> friend class Immutable;
     template <class S, class... Args> friend Mutable<S> makeMutable(Args&&...);
+    template <class S, class U> friend Mutable<S> staticMutableCast(const Mutable<U>&);
 };
 
 template <class T, class... Args>
@@ -46,6 +47,11 @@ Mutable<T> makeMutable(Args&&... args) {
     return Mutable<T>(std::make_shared<T>(std::forward<Args>(args)...));
 }
 
+template <class S, class U>
+Mutable<S> staticMutableCast(const Mutable<U>& u) {
+    return Mutable<S>(std::static_pointer_cast<S>(u.ptr));
+}
+
 /**
  * `Immutable<T>` is a non-nullable shared reference to a `const T`. Construction requires
  * a transfer of unique ownership from a `Mutable<T>`; once constructed it has the same behavior