Procedural macros

---

• procedural macros
• Apparently the Macro needs to be in its own Crate separate from where it is being used.

• Add proc-macro to the Cargo.toml

• Here we show that the macro is executed during the compilation.
• It needs to return a TokenStream.

examples/macros/hello-world-macro/Cargo.toml

[package]
name = "hello-world-macro"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[lib]
proc-macro = true

[dependencies]

examples/macros/hello-world-macro/src/lib.rs

extern crate proc_macro;
use proc_macro::TokenStream;

#[proc_macro]
pub fn hello_world(_item: TokenStream) -> TokenStream {
    println!("Hello World during compilation");

    //"println!(\"Hello World that was added to the code\");".parse().unwrap()
    r#"println!("Hello World that was added to the code");"#.parse().unwrap()
}

examples/macros/hello-world-use/Cargo.toml

[package]
name = "hello-world-use"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
hello-world-macro = { version = "0.1.0", path = "../hello-world-macro" }

examples/macros/hello-world-use/src/main.rs

extern crate hello_world_macro;
use hello_world_macro::hello_world;

fn main() {
    hello_world!();
}