On 10/11/2011 11:58, Basile Starynkevitch wrote:
Hello All
(I am playing with C++11, but I am not a C++ expert, and I don't know the C++
front-end
part of GCC, so this is a feature wish only).
Perhaps it could be useful for some later (4.8?) release of GCC to produce an
inferred
type annotation file.
For those knowing Ocaml, I was thinking of something similar to the -annot (or
-dtypes)
option of the ocaml or ocamlopt compiler.
http://caml.inria.fr/pub/docs/manual-ocaml/manual022.html
For instance with the simplistic (single line) Ocaml file incr.ml:
let f x = x + 1;;
the incr.annot file obtained with ocamlc -annot incr.ml contains
#######
"incr.ml" 1 0 4 "incr.ml" 1 0 5
type(
int -> int
)
ident(
def f "incr.ml" 1 0 15 "_none_" 1 0 -1
)
"incr.ml" 1 0 6 "incr.ml" 1 0 7
type(
int
)
ident(
def x "incr.ml" 1 0 10 "incr.ml" 1 0 15
)
"incr.ml" 1 0 10 "incr.ml" 1 0 11
type(
int
)
ident(
int_ref x "incr.ml" 1 0 6 "incr.ml" 1 0 7
)
"incr.ml" 1 0 12 "incr.ml" 1 0 13
type(
int -> int -> int
)
ident(
ext_ref Pervasives.( + )
)
"incr.ml" 1 0 14 "incr.ml" 1 0 15
type(
int
)
"incr.ml" 1 0 10 "incr.ml" 1 0 15
type(
int
)
############
and external editors (in particular the ocaml or tuareg modes of Emacs) are
able to parse
such annotation file, and interactively to show the type (with Ctrl-C Ctrl-T
under
emacs) at the cursor's position.
The main motivation would be to help C++ newbies, not C++ experts (those know
well
enough the C++ language, and don't need help). With the type inference
abilities given by
the auto keyword, it is sometimes hard for a beginner to understand what type
is some
particular expression in his code (or what exactly function is called in an
overloaded
context). The type annotation file can be generated by C++ front-end, and would
contain
type and position information for every expression inside a source file.
That type annotation produced by g++ would be usable by external editors, etc.
Of course, such a thing could be done by some GCC plugin, but I believe
providing the
feature inside GCC itself, and documenting the format of the textual type
annotation
file, would give this feature more visibility, and it would help people a lot.
And I am
pretty certain that the C++ frontend does compute the type of each expression,
so it is
mostly the point of defining a textual type annotation format and output it.
The point is that inside languages with type inferences, like C++ is becoming
in its 2011
standard, newbies are helped a lot with type annotations (and the editor's
support of
them) - but experts rarely need this.
So I would dream of a -fannotate-type option to g++ 4.8 with a section in the
documentation describing the format of the type annotation file.
We already have -M (etc..) options to help about include dependencies. We
could have
some other option to help about type inferences.
Regards.
I don't know why you say such a feature would only help C++ newbies - my
guess is that it would be at least as helpful to experts. But maybe
/real/ C++ experts have a different opinion there!
You might get something useful from the "-fdump-" options:
<http://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html>
I don't know which pass would be best for you, and obviously the use in
an editor depends entirely on the editor.
