Created attachment 343576 [details]
add support for null-conditional operators

C# 6.0 supports null-conditional operators "?." and "?[", and developers can handle assigning value to local variable (for thread safety), null-check and method invocation (or member access) with them easily.

  obj?.call_method ();

Preceding expression can be translated into the following lines.

  var local = obj;
  if (local != null) {
    local.call_method ();
  }

For more description, please see here. (https://msdn.microsoft.com/en-us/library/dn986595.aspx)

Attached patch includes implementations of null-conditional operators on vala.