C++ Preprocessors in Rust?

[unkempt bloom]

I was wondering if there is an equivalent for the following code in rust:

#ifdef DEBUG
#define Log(x) std::cout << x << std::endl
#else
#define Log(x)
#endif

[placid fern]

We don't have a C preprocessor, but you can do this. Since Rust tends to prefer functions whenever possible, you can write

#[cfg(debug_assertions)] //cfg = conditional compilation flag
fn log<T: Debug>(elem: T) {
  println!("{elem:?}");
}
#[cfg(not(debug_assertions))]
fn log<T: Debug>(elem: T) {}
```If you want to use macros instead, they work the same, you can put `cfg` on them too.

If you have a complex cfg chain, use the cfg-if crate, the "basic" syntax can be unwieldy

[unkempt bloom]

Thank you!
Can you write the same example with macros?
I want to understand how you do it in both ways 🙂

[placid fern]

#[cfg(debug_assertions)]
macro_rules! log {
  ($e:expr) {
    println!("{:?}", $e),
  }
}
#[cfg(not(debug_assertions))]
macro_rules! log {
  ($e:expr) {}
}