Comments on: tee: Debug Info With Little Impact On Code

By: fievel

fievel — Fri, 31 Aug 2018 10:06:00 +0000

In reply to sv90.

Yes I adapted this very useful snippet with
#define TEE(x) tee(__FILE__, __LINE__, #x, (x))

Now let see if my manager agree I submit that to codebase

By: sv90

sv90 — Fri, 29 Sep 2017 13:19:00 +0000

In reply to Jonathan Boccara. In principle, one could also use the __FILE__ and __LINE__ macros to get even more informations.

By: Jonathan Boccara

Jonathan Boccara — Fri, 29 Sep 2017 13:11:00 +0000

In reply to Gerald Squelart. Good point! I worked it into the article, thanks.

By: Jonathan Boccara

Jonathan Boccara — Fri, 29 Sep 2017 13:11:00 +0000

In reply to Sergio Adán. Didn't think about using runtime polymorphism with std::ostream here. Thanks for sharing this idea!

By: Jonathan Boccara

Jonathan Boccara — Fri, 29 Sep 2017 13:07:00 +0000

In reply to sv90. Very interesting, thanks for sharing!

By: Jonathan Boccara

Jonathan Boccara — Fri, 29 Sep 2017 13:06:00 +0000

In reply to Luis Antonio Donoso de Dios.

Hey Luis, you’re right, this allows to have a unique interface for const and non-const arguments.

If we pass an object to the implementation at the top then it makes a copy and returns it, which is not the purpose of a logger. And even if we change it and make it return a const reference then we can no longer pass it a non-const reference without having it constified. This is no the point of the logger either.

The forwarding reference allows to keep whatever const + l/r value semantics of the argument passed.
Hope I’m making sense here 🙂

By: sv90

sv90 — Fri, 29 Sep 2017 06:39:00 +0000

When using logging like this i like to also see the name of logged variable or expression. So I would maybe rewrite the second version as
“`
namespace detail {
template
decltype(auto) tee(const char* name, T&& val) noexcept {
std::clog << name << " = " << val << 'n';
return std::forward(val);
}
} // namespace detail

#define TEE(x) detail::tee(#x, (x))
“`
One could also wrap the macro inside some kind of `#ifndef` to deactivate logging with one variable.

By: Sergio Adán

Sergio Adán — Fri, 29 Sep 2017 06:15:00 +0000

I preffer to avoid templates to set up the stream. You will be unable to change the stream at runtime if it is set as a template parameter. Something like this (simplified version): https://wandbox.org/permlink/lXEMwmrRBgkQa8AU

This solution allows you to change between different output streams at runtime and even use multiple streams (with few changes) at the same time without changing anything in the code.

By: Luis Antonio Donoso de Dios

Luis Antonio Donoso de Dios — Fri, 29 Sep 2017 04:36:00 +0000

Please, could you elaborate which cases are not covered by the first version of `tee`? Is it to do with the constness of the argument?

By: Gerald Squelart

Gerald Squelart — Fri, 29 Sep 2017 02:21:00 +0000

For those stuck with C++11, where `decltype(auto)` is not available, use `auto f() -> return_type`, e.g.:

auto tee(T&& value) -> decltype(std::forward(value))