Rangesv3 pipe operator broken

Question

I have a vector of ints and I'd like to print it as a comma separated list. I would like to do it using ranges and since clang doesn't the necessary features I'd like to use rangesv3:

https://godbolt.org/z/esM5sPe6a

    std::vector<int> v{6, 2, 3, 4, 5, 6};


    // doesn't compile
    std::cout << (
        v | ranges::transform_view( [](int val){return fmt::format("{}",val);}) 
          | ranges::join_with_view(", ")
          | ranges::to<std::string>)
    ) << std::endl;

This doesn't compile and gives me some template deduction error. However

    // works
    auto a = ranges::transform_view(v,  [](int val){return fmt::format("{}",val);});
    std::cout << (ranges::join_with_view(a, ", ") | ranges::to<std::string>) << std::endl;

If I don't pipe v in, but instead pass it as an argument and do the same for the transformed range it works.

What am I doing wrong? I am the only one likes ranges, but finds the cumbersome due to these kind of problems?

To help people answer your question, you'll need to be more specific about the error. Please [edit] your post to incorporate the exact errors you get from your [mcve] (preferably using copy+paste to avoid transcription errors). — Toby Speight, Aug 31 '23 at 13:24
Also, your code is incomplete; in particular, it seems to be missing a `main()` function and at least one `#include`. Please [edit] your code so it's a [mcve] of your problem (including any necessary inputs, but preferably not needing any), then we can try to reproduce and solve it. You should also read [ask]. — Toby Speight, Aug 31 '23 at 13:25

康桓瑋 · Accepted Answer · 2023-08-31T13:22:40.180

ranges::transform_view is a class, which is an implementation detail of the range adaptor ranges::views::transform.

Only range adaptors can be composed via the pipe operator, so those under the namespace ranges::views are the ones you should use, for example:

std::cout << (
    v | ranges::views::transform( [](int val){return fmt::format("{}",val);}) 
      | ranges::views::join(", ")
      | ranges::to<std::string>
) << std::endl;

In general, you should always prefer views::meow.

Rangesv3 pipe operator broken

1 Answers1