New command: \__kernel_set_arg_to_keyvalue:Nnn about latex2e

[muzimuzhi]

I interpret your need as "exposing the logic of = argument modifier in ltcmd module as a public latex3 conditional function, which checks whether an n-type argument is in key-value format or not in the same way = modifier does". (The documentation of = modifier can be found in texdoc usrguide (2023-05-23), sec. 2.9 "Auto-converting to key–value format".)

I think the quickest way is implementing a modified version of \__cmd_arg_to_keyvalue:nn in your code.

Can you give some precise use cases which are not covered by = modifier?

[Sophanatprime]

The main reason is document command is rather slower than a usual macro, it executes many unnecessary codes for this demand.

\documentclass{article}

\ExplSyntaxOn
\cs_new:Npn \__kernel_set_arg_to_keyvalue:Nnn #1#2#3
  {
    \__cmd_arg_to_keyvalue:nn {#2} {#3}
    \tl_set_eq:NN #1 \ProcessedArgument
  }
\tl_new:N \l__my_keyvalue_tl
\scan_new:N \s__my_mark
\cs_new_protected:Npn \__my_if_keyvalue:nTF #1#2#3
  {
    \__kernel_set_arg_to_keyvalue:Nnn \l__my_keyvalue_tl { \s__my_mark } {#1}
    \str_if_eq:eeTF { \s__my_mark } { \tl_head:N \l__my_keyvalue_tl }
      {#3} {#2}
  }
\NewDocumentCommand \__mz_if_keyvalue:nTF { ={\s__my_mark} +m +m +m }
  {
    \str_if_eq:eeTF { \s__my_mark } { \tl_head:n {#1} }
      {#3} {#2}
  }
\ExplSyntaxOff
\usepackage{l3benchmark}
\begin{document}

\ExplSyntaxOn
\benchmark_tic:
\prg_replicate:nn { 10000 }
  { \__my_if_keyvalue:nTF {aa=b,hudiw=dwuiahud,ajwdihfuawijdaodhawdfe,aa=b } {}{} }
\benchmark_toc:

\benchmark_tic:
\prg_replicate:nn { 10000 }
  { \__mz_if_keyvalue:nTF {aa=b,hudiw=dwuiahud,ajwdihfuawijdaodhawdfe,aa=b } {}{} }
\benchmark_toc:

\benchmark_tic:
\prg_replicate:nn { 10000 }
  { \__my_if_keyvalue:nTF {aa=b,hudiw=dwuiahud,ajwdihfuawijdaodhawdfe,aa=b } {}{} }
\benchmark_toc:

\benchmark_tic:
\prg_replicate:nn { 10000 }
  { \__mz_if_keyvalue:nTF {aa=b,hudiw=dwuiahud,ajwdihfuawijdaodhawdfe,aa=b } {}{} }
\benchmark_toc:
\ExplSyntaxOff

\end{document}

and the result is

(l3benchmark) + TOC: 0.305 s %% plain macro
(l3benchmark) + TIC
(l3benchmark) + TOC: 0.678 s %% document command
(l3benchmark) + TIC
(l3benchmark) + TOC: 0.311 s %% plain macro
(l3benchmark) + TIC
(l3benchmark) + TOC: 0.664 s %% document command

in my laptop (with pdflatex). Of course, for longer arguments, the gap has narrowed.

[muzimuzhi]

BTW \__kernel... is still an internal name. \cmd_... is OK but I doubt LaTeX2e kernel will provide such one in short term.

[josephwright]

At present, the use case here does not really seem to justify adding this: yes document commands are slower than 'raw' macros, but there are reasons.