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# Error code E0320

Recursion limit reached while creating drop-check rules.

Example of erroneous code:

    #![allow(unused)]
    fn main() {
    enum A<T> {
        B,
        C(T, Box<A<(T, T)>>)
    }

    fn foo<T>() {
        A::<T>::B; // error: overflow while adding drop-check rules for A<T>
    }
    }

The Rust compiler must be able to reason about how a type is `Drop`ped, and by extension the types of its fields, to be able to generate the glue to properly drop a value. The code example above shows a type where this inference is impossible because it is recursive. Note that this is not the same as E0072, where a type has an infinite size; the type here has a finite size but any attempt to `Drop` it would recurse infinitely. For more information, read the `Drop` docs.

It is not possible to define a type with recursive drop-check rules. All such recursion must be removed.