On 2018-04-09 18:39, Cym13 wrote:
On Monday, 9 April 2018 at 15:30:33 UTC, Stefan Koch wrote:
On Friday, 6 April 2018 at 21:45:45 UTC, Zach Tollen wrote:
I think Walter's reason was that such macros would hide too many
idiosyncrasies in how they were programmed, such that a lot of code
which seems simple on the surface will actually obfuscate complicated
and arbitrary macro-programming patterns. Thus, code that uses them
will become much less maintainable, because it is liable to do so
many different and hidden things. Also, the tasks for which
AST-macros would typically be used are already largely accommodated
by templates and other features. Thus, the real need for them isn't
I think it's time to revisit this.
The reason being that templates are only well suited to very specific
types of meta-programs which have a low degree of parameterization and
a low degree of abstraction.
Using templates to introspect and manipulate types is like using a
hammmer's flat back to remove a nail.
It _can_ be done but with an absurd amount of work.
You just have to remove all of the wall around the nail by pounding it
until the wall has around the nail is disintegrated :)
This is not an exaggeration.
Templates used for introspection (or anything else really that's
modestly complex) are equally hard to reason about for compilers and
for programmers. I guess programmers have an advantage when it comes
to _efficient_ pattern recognition.
Wouldn't AST macros require either to standardize (and freeze) AST
representation within the compiler or to maintain an equally frozen
alternate representation to be exposed?
Yes. It can have two separate ASTs, one internal for the compiler and
one external that are used together with the AST macros. They would
probably quite similar but they don't need to be exactly the same.
I can't see how that wouldn't
make the compiler's development slower since all of a sudden changing
the internal representation would impact user code, especially given the
low number of breaking changes that are accepted today.
We already have three clients using the AST: LDC, GDC and the DMD Dub