Adds empty dbg calls

[DerekCresswell]

This allows users to call dbg() with no arguments to print out dummy text "dbg call reached".
Works with or without DBG_MACRO_DISABLE being defined.
Closes #64

[sharkdp]

Thank you very much for your contribution!

I didn't know that this would require us to add a lot of preprocessor macro code 🙁.

If we decide to add all of these tricks, (just) to support empty dbg() statements, do you think that there is a way to also make this compatible with #2?

[DerekCresswell]

@sharkdp I will change the print function to remove that duplication.

As for the macro, there really is not a way to do this with pre-processor statements other than to count the VA. Though adding other number of variables should be trivial. I.E.

#define dbg_x(x, A, B, Func, ...) Func
// ---
#define dbg_2(A, B) // ---
// ---
#define dbg(...) dbg_x(, ##__VA_ARGS__, dbg_VA(__VA_ARGS__), dbg_2(__VA_ARGS__),dbg_0())

This should not greatly affect the ability to implement #2 but I can attempt to look into it more. The only possible "snag" I see is needing defining a dbg_1(A).
This does what we need for now and shouldn't change the future much.

[DerekCresswell]

Alright @sharkdp the duplicate code is gone.
I've looked at the printing two arguments and am quite confident I could get it to work. Only thing is because of the lack of recursion for macros it will be like what I have here just expanded. It might look fairly ugly and become less readable.
I believe we should mostly ditch #2 as it will create a messy code base, though I will see if I can come up with something nice. I also think the functionality of empty calls is better than that of 2 arguments.

Let me know if you have more questions or concerns.

[sharkdp]

I've looked at the printing two arguments and am quite confident I could get it to work. Only thing is because of the lack of recursion for macros it will be like what I have here just expanded. It might look fairly ugly and become less readable.
I believe we should mostly ditch #2 as it will create a messy code base, though I will see if I can come up with something nice. I also think the functionality of empty calls is better than that of 2 arguments.

To be honest, for me, the multiple-arguments-dbg-call would be more interesting than than the zero-argument-dbg-call.

We did have an implementation for multiple arguments in #8 (which I needed to roll back because it broke some tests). It's not pretty, but I as you also said, there is no other way apparently. Ideally, this preprocessor code will not have to be touched in the future, as soon as we have support for 0 or more arguments.

The limitation to a certain maximum number of arguments wouldn't be any problem, in my point of view.

Thank you very much for looking into this!

[DerekCresswell]

@sharkdp Would you like me to try and put multiple arguments onto this as #64 and #2 do go hand in hand?
Say 0, 1, and 2 arg macros? How many would we want? How would they printout, just a print() for each one?

Or is there another issue / feature that'd be a better use of time here? I'm asking because I really enjoy this repo and would love to start actually working on repos other than mine :)

[sharkdp]

@sharkdp Would you like me to try and put multiple arguments onto this as #64 and #2 do go hand in hand?

That would be fantastic.

Say 0, 1, and 2 arg macros? How many would we want?

I would hope that if 0, 1 and 2 are possible, we could also add a few more lines to support 5 or 10.

How would they printout, just a print() for each one?

One line for each argument. Just as if the user had called dbg(arg1); dbg(arg2); dbg(arg3);. In an expression, the last argument would be returned. So basically, dbg(arg1, arg2, arg3) would be equivalent to dgb(arg1), dbg(arg2), dbg(arg3).

[sharkdp]

Here is the error:

C:\projects\dbg-macro\tests\example.cpp(28): error C2059: syntax error: ')' [C:\projects\dbg-macro\build\dbg_macro-example.vcxproj]
C:\projects\dbg-macro\tests\example.cpp(28): error C3553: decltype expects an expression not a type [C:\projects\dbg-macro\build\dbg_macro-example.vcxproj]
C:\projects\dbg-macro\tests\example.cpp(28): error C2947: expecting '>' to terminate template-argument-list, found '>' [C:\projects\dbg-macro\build\dbg_macro-example.vcxproj]

Looks like this doesn't work on MSVC.

[sharkdp]

(I fixed some merge conflicts)

With clang, I get a lot of warnings:

/home/shark/Dropbox/Informatik/c++/dbg-macro/./dbg.h:570:24: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
#define dbg(...) dbg_x(, ##__VA_ARGS__, dbg_VA(__VA_ARGS__), dbg_0())

[sharkdp]

On gcc, I also get some warnings:

/home/shark/Dropbox/Informatik/c++/dbg-macro/tests/tests.cpp: In function ‘int main()’:
/home/shark/Dropbox/Informatik/c++/dbg-macro/tests/tests.cpp:137:27: warning: statement has no effect [-Wunused-value]
  137 |   dbg(std::vector<int>{0, 1, 0, 1});
      |                           ^
/home/shark/Dropbox/Informatik/c++/dbg-macro/./dbg.h:566:32: note: in definition of macro ‘dbg_x’
  566 | #define dbg_x(x, A, Func, ...) Func
      |                                ^~~~
/home/shark/Dropbox/Informatik/c++/dbg-macro/tests/tests.cpp:137:3: note: in expansion of macro ‘dbg’
  137 |   dbg(std::vector<int>{0, 1, 0, 1});
      |   ^~~

I'm beginning to think that we should simply omit this feature 🙁

[DerekCresswell]

I'm beginning to think that we should simply omit this feature

Let me keep at her a bit longer, don't lose hope. A lot of warnings are because compilers do not like (, ##__VA_ARGS__) even though they support it. I'll find a way. Got my windows laptop now too.

[sharkdp]

Any update on this? Otherwise, I'd like to close it.

[DerekCresswell]

Sadly no, been neglecting this : (. I'd say keep the issue open though.

[sharkdp]

No worries, thank you for the update. We'll keep the issue open, yes. The PR here is not lost either.