[megumax]

POSIX is not ISO C or C++ standard. On Windows, what are you gonna do?

Also, other languages are Rust, Kotlin, Swift (to name a few `modern` ones). Yes, Kotlin and Swift have `first class` CLI parsing libraries, but they are not part of standard library.

[morelisp]

"First-party" is distinct from "first class". The difference between a first-party library and the standard library ranges from "slightly weaker compatibility guarantees" to "it's supported in all environments where it makes sense, but the language can run unhosted so that's not everywhere" to "no difference at all, we just didn't want to package it with the compiler".

You're also missing the forest for the "well actually" trees: Lots of languages have argument parsing in their stdlib.