[cfe-dev] Clarification for term "AST"
pidgeot18 at gmail.com
Sun Feb 24 11:59:13 PST 2013
On 2/24/2013 5:38 AM, Markus Elfring wrote:
>> I can't say that I can think of a single time where I would ever want
>> the raw parsed AST with no semantic analysis done on it.
> Are you interested in detailed source code transformations after a
> specific analysis on a control flow graph?
> Do you see use cases to drill down from higher abstraction levels to
> the abstract syntax tree to generate some adjustments?
The short answer here is "no", because viewing refactorings as
transformations on ASTs is wrong. Refactoring is really transforming
source text to source text guided by high-level semantic rules; treating
it as AST implementations will cause lots of grief when you try to
reserialize that AST, thanks in large part to the complications of
macros and templates (macros++).
> How do you think about consequences and challenges like they are
> demonstrated by the semantic patch language from the software
Semantic patching is very seductive, but it's a poor substitute when it
comes to complicated refactorings. The use case I played with a few
years ago was rewriting a C API into C++, which requires some semantic
rules cumbersome to produce in an spatch-like format. The best example I
have is "make the first argument to be 'derived' from MimeObject be the
implicit this argument." Another one is "every object which is the
implicit this argument cast to some other type is really just the
implicit this argument, if the cast is a cast to the current class type
or some superclass thereof".
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