My new favorite way to represent AST's (or any recursive type really) in rust

For a long time i represented my Abstract Syntax Trees like so

pub enum AST{
    Application(Box<(AST,AST)>),
    Abstraction(Box<(AST,AST)>),
    Variable(usize)
}

Recently i discovered another way. Instead of having an enum i could lift AST into a trait and variants to its own structures.

pub struct Application<Fun:AST, Args:Ast>( Fun,Args)
pub struct Abstraction<Body:Ast>( Variable,Body)
pub struct Variable(usize)

pub trait AST {
    // ... fill your methods here
}

impl <Fun:AST, Args:Ast> AST for Application<Fun,Args>{}

impl <Body:AST> AST for Abstraction<Body>{}

impl AST for Variable{}

The nice thing here is that we got rid of the pesky \``Box\\ and stronger typing requirements \[look at Abstraction\] (although the last point could've been made with regular enums as well).

Anyways I just wanted to share this