If you want to use a tool that pastes code fragments in arbitrary places you can. However, I'm not clear on the benefit over something that's aware of its context, or at the very least AST aware.

Even modern C++ has eschewed macros for virtually every use case, the only reason I've had to use them (legitimately) has been conditional compilation and some compiler/platform specific issues.

Like if you're doing #define PI 3.14159 you're asking to get chirped in code review.

Just because we don't have textual substitution doesn't mean we don't have macros. We have a lot of macros!

(It took me a while to write back to you because I am busy writing bare-metal embedded Rust, btw. Including using some macros!)

A proc macro would still need to be invoked as either

    cpp_call! { fn foo() { ... } }

or

   #[cpp_call] fn foo() { ... }

The former can be written even with a macro_rules macro. Regardless, both macros have to work by parsing the whole input tokentree `fn foo ( ) { ... }` and emitting it back with an `unsafe` prepended. The macro invocation cannot expand to just `unsafe`.

its splitting hairs but not really. Rust's proc macros need to be explicitly invoked using special syntax at the usage site, either by annotating a statement or enclosing a block of tokens. On top of that, they do token replacement (or addition, with derive macros) which means they can only take valid input tokens as an argument (compared to macro_rules which can take arbitrary strings).

Textual substitution is less rigorous. It tells the compiler to replace a string with another, wherever it is seen. There's no restriction that it must be valid token input to be replaced or that it needs to be an explicit usage of the macro.

> Except for the fact that they do not allow emitting invalid token streams (which is something you don't want anyways)

Reminds me of some of stringification abused in the Linux kernel. What looks like a function call passing the literal text param1## as an argument, where it would then trigger a different stringification in a subsequent preprocessor pass that prepended ##foo to the passed argument.

Nature finds its ways.

Seriously though, maybe comment annotation would be better than abusing the macros like that. I though there was a more direct cpp way. (Edit: As in the c preprocessor, not C++.)