struct Context {
    timestamp: u64,
}

struct Untrusted;
struct Validated<'c> {
    ctx: &'c Context,
}

struct User {
    counter: u64,
    ctx: Context
}

impl Context {
    fn validate<'c>(&'c self, _input: Untrusted) -> Validated<'c> {
        Validated { ctx: self }
    }
}

impl User {
    fn consume<'c>(&'c mut self, valid_input: Validated<'c>) {
       self.counter += 1;
    }
}

fn main() {
    let mut user = User{ ctx: Context{timestamp: 42}, counter: 0};
    let valid = user.ctx.validate(Untrusted{});
    user.consume(valid);
    println!("ok")
}