Recently I spent some time to write a DSL ( domain specific Language) lexer and parser.
Without double flex, bison (C++) will be used. Bison ( version 3.0.2/3.04) generally support C++ object as the semantics value. That is a good thing since we do not need %destructor to enable memory deallocation during error recovery; the memory, for strings for instance, will be reclaimed by the regular destructors.
But when we want to create a large C++ object while parsing, we want to pass pointers instead of copying object. The raw new/delete is urgly, thus naturally we want to use std::unique_ptr as the semantics value. Since std::unique_ptr is a object, bison C++ should support it, right?
It turned out that Bison 3.0.3/3.0.4 does not support well using std::unqiue_ptr as semantic value. It can not even compile, it need one hack! we need to replace one line with std::move, thanks Sasah ( from bison mailing list)! !
— file.hh
+++ file.hh
@@ -178 +178 @@
– return *new (yyas_<T> ()) T (t);
+ return *new (yyas_<T> ()) T (std::move((T&)t));
we can use sed to replace it: sed -i ‘s/return \*new (yyas_<T> ()) T (t)/return \*new (yyas_<T> ()) T (std\:\:move((T\&)t))/’ your_file.hh
Now it compiles, and the parser works.
More details can be see at:
http://lists.gnu.org/archive/html/help-bison/2016-08/msg00014.html
http://lists.gnu.org/archive/html/bug-bison/2016-08/msg00006.html.
Hopefully in the future bison will officially support the std::unique_ptr!
