start config maybe

src/ext.rs

@@ -1,6 +1,9 @@
 use super::*;
 use std::{
     io::{self, Read, Write},
+    any::Any,
+    marker::{Send, Sync},
+    fmt,
 };
 
 pub trait Tuple2Ext<T,U>: Sized
@@ -109,3 +112,16 @@ impl<R: io::Read> IOCounterReadExt for R
     }
 }
 
+/// A boxed `'static` value of anything anything that is `Send` and `Sync`.
+#[repr(transparent)]
+pub struct Anything(pub Box<dyn Any + Send + Sync + 'static>);
+
+impl fmt::Debug for Anything
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+    {
+	write!(f, "<opaque object>: (at: {:p}, sz: {})",
+	       Box::as_ref(&self.0),
+	       std::mem::size_of_val(Box::as_ref(&self.0)))
+    }
+}

src/formats.rs

@@ -11,7 +11,12 @@ use object::Object;
 mod json;
 
 /// Config for the encode/decode
-pub struct Config; //TODO: What goes here?
+#[derive(Debug)]
+pub struct Config{
+    //TODO: What goes here?
+    /// Any arbitrary data.
+    pub user: Option<Anything>,
+} 
 
 /// A directive for a format on how to encode and decode objects.
 #[derive(Clone, Copy)]