Distracting syntax highlighting
By David Röthlisberger. Comments welcome at david@rothlis.net.
Last updated 10 Nov 2011. This article is Creative Commons licensed.
Code sample taken from SGI’s implementation of the C++ standard template library.
Eclipse’s default syntax highlighting seems to thinks that the language’s keywords are the most important part of a C++ program. Template! Class! Public! Typedef! Const! Return! It might not seem that hard to pick out the class and member names from the wall of code below, but when working with unfamiliar code all day, the effort does drain me.
The colour scheme that ships with Emacs isn’t any better — I find its rainbow effect rather distasteful, more distracting than helpful.
The right-most column below shows what I’ve been using in my day-to-day work. It aims to be a simple, unobtrusive colour scheme that highlights the declarations and definitions of classes, members, and variables.
Eclipse
// Base class for ordinary allocators. template <class _Tp, class _Allocator, bool _IsStatic> class _Vector_alloc_base { public: typedef typename _Alloc_traits<_Tp, _Allocator>::allocator_type allocator_type; allocator_type get_allocator() const { return _M_data_allocator; } _Vector_alloc_base(const allocator_type& __a) : _M_data_allocator(__a), _M_start(0), _M_finish(0), _M_end_of_storage(0) {} protected: allocator_type _M_data_allocator; _Tp* _M_start; _Tp* _M_finish; _Tp* _M_end_of_storage; _Tp* _M_allocate(size_t __n) { return _M_data_allocator.allocate(__n); } void _M_deallocate(_Tp* __p, size_t __n) { if (__p) _M_data_allocator.deallocate(__p, __n); } }; // Specialization for allocators that have the property that we don't // actually have to store an allocator object. template <class _Tp, class _Allocator> class _Vector_alloc_base<_Tp, _Allocator, true> { public: typedef typename _Alloc_traits<_Tp, _Allocator>::allocator_type allocator_type; allocator_type get_allocator() const { return allocator_type(); } _Vector_alloc_base(const allocator_type&) : _M_start(0), _M_finish(0), _M_end_of_storage(0) {} protected: _Tp* _M_start; _Tp* _M_finish; _Tp* _M_end_of_storage; typedef typename _Alloc_traits<_Tp, _Allocator>::_Alloc_type _Alloc_type; _Tp* _M_allocate(size_t __n) { return _Alloc_type::allocate(__n); } void _M_deallocate(_Tp* __p, size_t __n) { _Alloc_type::deallocate(__p, __n);} }; template <class _Tp, class _Alloc> struct _Vector_base : public _Vector_alloc_base<_Tp, _Alloc, _Alloc_traits<_Tp, _Alloc>::_S_instanceless> { typedef _Vector_alloc_base<_Tp, _Alloc, _Alloc_traits<_Tp, _Alloc>::_S_instanceless> _Base; typedef typename _Base::allocator_type allocator_type; _Vector_base(const allocator_type& __a) : _Base(__a) {} _Vector_base(size_t __n, const allocator_type& __a) : _Base(__a) { _M_start = _M_allocate(__n); _M_finish = _M_start; _M_end_of_storage = _M_start + __n; } ~_Vector_base() { _M_deallocate(_M_start, _M_end_of_storage - _M_start); } };Emacs
// Base class for ordinary allocators. template <class _Tp, class _Allocator, bool _IsStatic> class _Vector_alloc_base { public: typedef typename _Alloc_traits<_Tp, _Allocator>::allocator_type allocator_type; allocator_type get_allocator() const { return _M_data_allocator; } _Vector_alloc_base(const allocator_type& __a) : _M_data_allocator(__a), _M_start(0), _M_finish(0), _M_end_of_storage(0) {} protected: allocator_type _M_data_allocator; _Tp* _M_start; _Tp* _M_finish; _Tp* _M_end_of_storage; _Tp* _M_allocate(size_t __n) { return _M_data_allocator.allocate(__n); } void _M_deallocate(_Tp* __p, size_t __n) { if (__p) _M_data_allocator.deallocate(__p, __n); } }; // Specialization for allocators that have the property that we don't // actually have to store an allocator object. template <class _Tp, class _Allocator> class _Vector_alloc_base<_Tp, _Allocator, true> { public: typedef typename _Alloc_traits<_Tp, _Allocator>::allocator_type allocator_type; allocator_type get_allocator() const { return allocator_type(); } _Vector_alloc_base(const allocator_type&) : _M_start(0), _M_finish(0), _M_end_of_storage(0) {} protected: _Tp* _M_start; _Tp* _M_finish; _Tp* _M_end_of_storage; typedef typename _Alloc_traits<_Tp, _Allocator>::_Alloc_type _Alloc_type; _Tp* _M_allocate(size_t __n) { return _Alloc_type::allocate(__n); } void _M_deallocate(_Tp* __p, size_t __n) { _Alloc_type::deallocate(__p, __n);} }; template <class _Tp, class _Alloc> struct _Vector_base : public _Vector_alloc_base<_Tp, _Alloc, _Alloc_traits<_Tp, _Alloc>::_S_instanceless> { typedef _Vector_alloc_base<_Tp, _Alloc, _Alloc_traits<_Tp, _Alloc>::_S_instanceless> _Base; typedef typename _Base::allocator_type allocator_type; _Vector_base(const allocator_type& __a) : _Base(__a) {} _Vector_base(size_t __n, const allocator_type& __a) : _Base(__a) { _M_start = _M_allocate(__n); _M_finish = _M_start; _M_end_of_storage = _M_start + __n; } ~_Vector_base() { _M_deallocate(_M_start, _M_end_of_storage - _M_start); } };Proposed colour scheme
// Base class for ordinary allocators. template <class _Tp, class _Allocator, bool _IsStatic> class _Vector_alloc_base { public: typedef typename _Alloc_traits<_Tp, _Allocator>::allocator_type allocator_type; allocator_type get_allocator() const { return _M_data_allocator; } _Vector_alloc_base(const allocator_type& __a) : _M_data_allocator(__a), _M_start(0), _M_finish(0), _M_end_of_storage(0) {} protected: allocator_type _M_data_allocator; _Tp* _M_start; _Tp* _M_finish; _Tp* _M_end_of_storage; _Tp* _M_allocate(size_t __n) { return _M_data_allocator.allocate(__n); } void _M_deallocate(_Tp* __p, size_t __n) { if (__p) _M_data_allocator.deallocate(__p, __n); } }; // Specialization for allocators that have the property that we don't // actually have to store an allocator object. template <class _Tp, class _Allocator> class _Vector_alloc_base<_Tp, _Allocator, true> { public: typedef typename _Alloc_traits<_Tp, _Allocator>::allocator_type allocator_type; allocator_type get_allocator() const { return allocator_type(); } _Vector_alloc_base(const allocator_type&) : _M_start(0), _M_finish(0), _M_end_of_storage(0) {} protected: _Tp* _M_start; _Tp* _M_finish; _Tp* _M_end_of_storage; typedef typename _Alloc_traits<_Tp, _Allocator>::_Alloc_type _Alloc_type; _Tp* _M_allocate(size_t __n) { return _Alloc_type::allocate(__n); } void _M_deallocate(_Tp* __p, size_t __n) { _Alloc_type::deallocate(__p, __n);} }; template <class _Tp, class _Alloc> struct _Vector_base : public _Vector_alloc_base<_Tp, _Alloc, _Alloc_traits<_Tp, _Alloc>::_S_instanceless> { typedef _Vector_alloc_base<_Tp, _Alloc, _Alloc_traits<_Tp, _Alloc>::_S_instanceless> _Base; typedef typename _Base::allocator_type allocator_type; _Vector_base(const allocator_type& __a) : _Base(__a) {} _Vector_base(size_t __n, const allocator_type& __a) : _Base(__a) { _M_start = _M_allocate(__n); _M_finish = _M_start; _M_end_of_storage = _M_start + __n; } ~_Vector_base() { _M_deallocate(_M_start, _M_end_of_storage - _M_start); } };Certainly different programmers will want different things from syntax
highlighting. When working with a new language, marking the language’s
reserved keywords can be helpful in remembering small details (is it
elif, elsif, or else if?), and in avoiding clashes between keywords
and variable names (in an interpreted language, such a clash might not be
noticed until run-time). But such a distinction can be done subtly, not
bold and red! When I’m working with a familiar language, I prefer the
keywords to blend into the background, as befits syntactical
implementation details.
An imperfect Emacs configuration follows. It is imperfect because the Emacs syntax highlighting engine doesn’t parse C++ 100% correctly, and doesn’t differentiate between a type’s definition and subsequent usages of the type.