On Tue, Apr 18, 2023 at 11:23:54AM -0400, Jason McKesson via Std-Discussion wrote:
>On Tue, Apr 18, 2023 at 8:58 AM Federico Kircheis via Std-Discussion
><std-discussion_at_[hidden]> wrote:
>>
>> On Tue, Apr 18, 2023 at 08:32:32AM -0400, Jason McKesson via Std-Discussion wrote:
>> >On Tue, Apr 18, 2023 at 7:53 AM Federico Kircheis via Std-Discussion
>> ><std-discussion_at_[hidden]> wrote:
>> >>
>> >> Hello, I have a question regarding std::format.
>> >>
>> >> The API works generally very well, but it is problematic to escape every
>> >> { and }, especially when there are a lot of those, like in json objects.
>> >>
>> >> Suppose I have for example the literal
>> >>
>> >> R"json({
>> >> "data": {
>> >> "data 1": [
>> >> {"id":1,"name":"foo"},
>> >> {"id":2,"name":"bar"}
>> >> ],
>> >> "data 2": {"id":2,"name":"____"}
>> >> },
>> >> "otherstuff": {
>> >> "void": [[1,42],[-1,____]]
>> >> }
>> >> })json"
>> >>
>> >> And I would like to use std::format for replacing ____ with some values.
>> >>
>> >> As far as I know, it is not possible to instruct std::format to use
>> >> another pair of delimiters for a single call.
>> >>
>> >> Falling back to std::printf or std::cout does not seem to be the right
>> >> solution, and escaping every { and } has drawbacks too.
>> >>
>> >> Was this issue ever discussed or acknowledged?
>> >> Are there some obvious workarounds I'm missing?
>> >
>> >No tool is going to be perfect for every application, and for basic
>> >tools like `format`, you have to pick *something* for your delimiter.
>> >
>> >Find/replace is not `format`'s job. That's the job of a regex tool.
>>
>> I suppose my choice of words was not ideal.
>> I did not want to say I want to replace ____ with a given value, ____ is
>> in this example the placeholder for the value one is going to format.
>>
>> I could obviously not use {} for describing the issue, maybe it would
>> have been better if I've used the std::printf syntax: %s and %d
>
>I'm confused. You say that you don't want to "replace ____ with a
>given value", but you then claim that "____" is "the placeholder for
>the value one is going to format".
>
>That's what "replace" means. You're telling `format` to search through
>the string for its formatting tags, and you want it to take any
>instance of that formatting tag and turn it into a value from one of
>its parameters. That's... replacing.

 From your previous reply I thought you thought I meant replacing the
substring ____ with another specific string.
std::format permits to specify how to format and convert the content, so
it is not a simple search and replace.

You did not meant that, ignore the mail where I substitute ____ with %s
and %d
>
>`std::format` and `std::printf` are both specialized versions of
>generic string find/replace operations. The principle specialization
>is that the text to be replaced is determined by the system, not by an
>arbitrary input to the system. That is, `format/printf` determines
>what strings it searches for.
>
>Your needs simply do not match the powers of the specialized tool.

Why not?

>Therefore, a more generalized tool is appropriate. Making `format`
>take different formatting tags adds complexity to a system that is
>otherwise quite functional for its intended purpose.