[cfe-dev] Adding support for Cloning in the AST

[Sebastian Redl]

moataz ragab wrote:
>
>
> On Sat, May 23, 2009 at 3:46 PM, Sebastian Redl
> <sebastian.redl at getdesigned.at <mailto:sebastian.redl at getdesigned.at>>
> wrote:
>
>     Douglas Gregor wrote:
>     >
>     > On May 19, 2009, at 7:18 PM, moataz ragab wrote:
>     >
>     >> Whether it might be useful or not to clone a declaration, it
>     might be
>     >> useful if you want to create a new variable declaration similar to
>     >> another declaration and only change the name.
>     >
>     >
>     > Hmmm, interesting. It seems to me like we really want to give the
>     > expression's Clone method some information that tells it what to do
>     > with declarations. For your loop-unrolling rewriter, we want to
>     > replace some variable declarations with other, similar variables
>     > (e.g., when the original variable was declared in the loop) or reuse
>     > the same variable declaration (if the variable is declared
>     outside the
>     > loop).
>
>
>    For the loop unrolling rewriter, I was thinking about skipping the
> declarations in loop body and replace them with an assignmen if they
> were initializing the variable. I planned to stop the cloning at this
> level and make the expression point to the same declaration.
> It doesn't come to my mind a case where I would need to declare
> another variable. Please correct me if I am wrong?
>
It's wrong in the case of C++ where initialization and assignment can
really differ. Sometimes one is possible, and the other isn't. The
simplest case is where the variable in question is a reference.
>
>     A callback to handle all sub-objects, instead of just cloning
>     recursively? It would be very tricky to do as a "policy" that is
>     anything less than a fully generic callback, given that cloning is
>     deep.
>     The callback has to handle everything in that part of the AST somehow.
>     You can't stop at a single level.  
>
>    What do you think about passing a visitor to Clone()?
It's probably what passing a callback comes down to.

Sebastian