Using back_inserter without the std:: prefix

[thraneh]

I have a custom container with appropriate iterators, push_back method, etc. This used to work up until fmt 10.0.2

I haven't yet been able to set up a minimal example to reproduce this.

However, the issue arise from this line where back_inserter is used without the std:: prefix (maybe you wanted to use your own invoke_back_inserter?)

• fmt/include/fmt/base.h

  Line 1098 in 9f0c0c4

  auto out() -> OutputIt { return back_inserter(container_); }

The issue was seen when compiling C++23

GCC 14.1.0 (Linux)

.../opt/conda/envs/dev/include/fmt/base.h:1089:48: error: 'back_inserter' was not declared in this scope; did you mean 'std::back_inserter'?
 1089 |   auto out() -> OutputIt { return back_inserter(container_); }
      |                                   ~~~~~~~~~~~~~^~~~~~~~~~~~
      |                                   std::back_inserter

Clang 18.1.8 (MacOS)

.../opt/conda/envs/dev/include/fmt/base.h:1089:35: error: use of undeclared identifier 'back_inserter'
 1089 |   auto out() -> OutputIt { return back_inserter(container_); }
      |

I can work around this by defining back_inserter in the global namespace before including any of the fmt headers.

[vitaut]

I think we could add using namespace std; just before calling back_inserter which would handle both ADL and std::back_inserter case. Could you submit a PR?

[thraneh]

I could submit a PR for that small change, but I'm lacking enough detailed knowledge about your library.

Clearly, you have a reason for preferring using namespace std; / back_inserter to simply using std::back_inserter.

In base.h there's a namespace adl which has invoke_back_inserter and otherwise does something similar to what you just suggested.

My problem is that an isolated PR with this small change just doesn't seem right. You have some idea behind the "adl" that I'm not familiar with.

[vitaut]

invoke_back_inserter is irrelevant here but in any case this is fixed in bf870ae in a slightly simpler way.