how to add new proc macro to existing structure StructA and impl so that we do not need create a new structure for StructA

To add a new proc macro to an existing structure StructA and its implementation, you can follow these steps:

1. Define the new proc macro function and implement it for StructA.

2. Update the impl block for StructA to include the new proc macro. This can be done by adding a new method to the impl block that calls the proc macro function.

Here's an example code snippet:

use proc_macro::TokenStream;

struct StructA {
    // existing fields and methods
}

impl StructA {
    fn existing_method(&self) {
        // existing method implementation
    }

    // new method using the proc macro
    #[my_proc_macro]
    fn new_method(&self) {
        // implementation provided by the proc macro
    }
}

// define the proc macro
#[proc_macro]
pub fn my_proc_macro(input: TokenStream) -> TokenStream {
    // implementation for the proc macro
}

In this example, we have added a new method new_method to the impl block for StructA. This method uses the proc macro my_proc_macro, which we have defined separately.

By adding the new method to the existing StructA and impl block, we do not need to create a new structure. We can simply use the updated StructA with the new method added