Cloning "anyhow::Error"

matklad · March 26, 2022, 6:24am

I think there’s a much more specific reason. Many errors (including io::Error) store a type-erased variant:

Box<dyn error::Error + Send + Sync>

Rust just doesn’t allow such dyn objects to be Clone or Eq in a nice way. Even if you add Clone and Eq to the Error’s super-traits, this won’t just extend to a trait object, you’ll have to do some extra dancing, like here:

github.com

near/nearcore/blob/525e5d67e4e0de691e88bfa0f869c69d795b1e41/runtime/near-vm-errors/src/lib.rs#L468


      
          }
          
          
impl Eq for AnyError {}
          
          
impl fmt::Debug for AnyError {
              fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                  fmt::Debug::fmt(self.any.as_any(), f)
              }
          }
          
          
trait AnyEq: Any + Send + Sync {
              fn any_eq(&self, rhs: &dyn AnyEq) -> bool;
              fn as_any(&self) -> &dyn Any;
              fn into_any(self: Box<Self>) -> Box<dyn Any>;
          }
          
          
impl<T: Any + Eq + Sized + Send + Sync> AnyEq for T {
              fn any_eq(&self, rhs: &dyn AnyEq) -> bool {
                  match rhs.as_any().downcast_ref::<Self>() {
                      Some(rhs) => self == rhs,
                      None => false,

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Cloning "anyhow::Error"

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