Method new

crates/core/src/error/error.rs:136–201

(mut error: E)

impl BoxedDynError {
    #[inline]
    fn new<E>(mut error: E) -> Result<Self, OutOfMemory>
    where
        // NB: This implies `Send + Sync`, which is necessary for safety.
        E: ErrorExt,
    {
        #[cfg(not(feature = "backtrace"))]
        let _ = &mut error;

        // Note: do not use `Option::or_else` here to avoid an extra frame
        // showing up in the backtrace, which would create extra noise for users
        // to mentally filter out.
        #[cfg(feature = "backtrace")]
        let backtrace = match error.take_backtrace() {
            Some(bt) => bt,
            None => crate::error::backtrace::capture(),
        };

        let boxed = try_new_uninit_box()?;
        let error = Box::write(
            boxed,
            ConcreteError {
                vtable: Vtable::of::<E>(),
                #[cfg(feature = "backtrace")]
                backtrace: Some(backtrace),
                error,
            },
        );

        // We are going to pun the `ConcreteError<E>` pointer into a `DynError`
        // pointer. Debug assert that their layouts are compatible first.
        #[cfg(debug_assertions)]
        {
            let dyn_size = mem::size_of::<DynError>();
            let concrete_size = mem::size_of::<ConcreteError<E>>();
            assert!(
                dyn_size <= concrete_size,
                "assertion failed: {dyn_size} <= {concrete_size}"
            );

            let dyn_align = mem::align_of::<DynError>();
            let concrete_align = mem::align_of::<ConcreteError<E>>();
            assert!(
                dyn_align <= concrete_align,
                "assertion failed: {dyn_align} <= {concrete_align}"
            );

            let dyn_offset = mem::offset_of!(DynError, vtable);
            let concrete_offset = mem::offset_of!(ConcreteError<E>, vtable);
            assert_eq!(dyn_offset, concrete_offset);

            #[cfg(feature = "backtrace")]
            {
                let dyn_offset = mem::offset_of!(DynError, backtrace);
                let concrete_offset = mem::offset_of!(ConcreteError<E>, backtrace);
                assert_eq!(dyn_offset, concrete_offset);
            }
        }