Add an evil ObjectClass::cast() helper

hdf5-rs/src/class.rs

@@ -1,4 +1,6 @@
use std::fmt;
use std::mem;
use std::ptr;

use crate::internal_prelude::*;

@@ -48,6 +50,13 @@ pub trait ObjectClass: Sized {
        &mut *(self as *mut Self as *mut T)
    }

    unsafe fn cast<T: ObjectClass>(self) -> T {
        // This method requires you to be 18 years or older to use it
        let obj = ptr::read(&self as *const _ as *const _);
        mem::forget(self);
        obj
    }

    fn debug_fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        // TODO: this can moved out if/when specialization lands in stable
        h5lock!({