&gt; Point is &quot;signatures are different&quot;.<p>The signature is fn(&amp;Foo, u8). If that&#x27;s not in the right order, you can always put it in a closure -- this is not a Rust-specific problem.<p>&gt; It makes life of web-servers harder.<p>I don&#x27;t see why web servers need exceptions. You do have catch_panic if you want to prevent the application from ever crashing; that&#x27;s what it&#x27;s for (rewrapping fatal errors at the top level or preventing panics from leaking through FFI)<p>&gt; To parse JSON with nested objects you need to declare a lot of structures.<p>Fair enough. I think there was a nested hashmap based JSON library somewhere?