c19: A custom derive macro that automatically implements a trait on a struct

Author: polyactis

c19_macro/Cargo.toml

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+workspace = { members = ["hello_macro", "pancakes"] }

c19_macro/hello_macro/Cargo.toml

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+#workspace = { members = ["hello_macro_derive"] }
+[package]
+name = "hello_macro"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

c19_macro/hello_macro/hello_macro_derive/Cargo.toml

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+[package]
+name = "hello_macro_derive"
+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]
+syn = "1.0"
+quote = "1.0"

c19_macro/hello_macro/hello_macro_derive/src/lib.rs

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+use proc_macro::TokenStream;
+use quote::quote;
+use syn;
+
+#[proc_macro_derive(HelloMacro)]
+pub fn hello_macro_derive(input: TokenStream) -> TokenStream {
+    // Construct a representation of Rust code as a syntax tree
+    // that we can manipulate
+    let ast = syn::parse(input).unwrap();
+    // Build the trait implementation
+
+    impl_hello_macro(&ast)
+}
+
+fn impl_hello_macro(ast: &syn::DeriveInput) -> TokenStream {
+    let name = &ast.ident;
+    let gen = quote!{
+        impl HelloMacroTrait for #name {
+            fn hello_macro() {
+                println!("Hello, Macro! My name is {}!", stringify!(#name));
+            }
+        }
+    };
+    gen.into()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn hello_macro_derive_works() {
+        //let result = add(2, 2);
+        //assert_eq!(result, 4);
+    }
+}

c19_macro/hello_macro/src/lib.rs

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+pub trait HelloMacroTrait {
+    fn hello_macro();
+}
+
+pub fn add(left: usize, right: usize) -> usize {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn hello_macro_test() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}

c19_macro/pancakes/Cargo.toml

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+[package]
+name = "pancakes"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+hello_macro = {path = "../hello_macro"}
+hello_macro_derive = {path = "../hello_macro/hello_macro_derive"}

c19_macro/pancakes/src/main.rs

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+use hello_macro::HelloMacroTrait;
+use hello_macro_derive::HelloMacro;
+
+
+#[derive(HelloMacro)]
+struct Pancakes;
+
+
+#[derive(HelloMacro)]
+struct Icecakes;
+fn main() {
+    println!("HelloMacro is a custom derivable macro that automatically implements trait HelloMacroTrait on a struct.");
+    Pancakes::hello_macro();
+    Icecakes::hello_macro();
+}