Skill tree for const eval features

g cell_ref references to interior mutability feature:const_cell_refs mut_ref mutable references in const fn feature:const_mut_refs const_mut_ref mutable references in initializers of const items const_mut_ref->mut_ref file_output write to files from constants final_heap heap allocations in the final value of constants heap heap allocations final_heap->heap heap->cell_ref heap->mut_ref trait_impl feature:const_trait_impl heap->trait_impl iterators iterators iterators->mut_ref iterators->trait_impl for for loops for->mut_ref for->trait_impl slice_eq [T]::eq slice_eq->for fuzzy-ptr-comparisons guaranteed_eq and guaranteed_ne feature:const_compare_raw_pointers slice_eq->fuzzy-ptr-comparisons slice_eq->trait_impl box_new Box::new box_new->heap trait_bound_opt_out feature:const_trait_bound_opt_out box_new->trait_bound_opt_out drop Drop box_new->drop ptr-is-null <*T>::is_null feature:const_ptr_is_null ptr-is-null->fuzzy-ptr-comparisons unconst_rules unconst operations raw_ptr_deref feature:const_raw_ptr_deref offset_of offset_of offset_of->raw_ptr_deref offset_from offset_from feature:ptr_offset_from offset_of->offset_from raw_ref_macros raw_ref maros feature:raw_ref_macros offset_of->raw_ref_macros maybe_uninit_as_ptr MaybeUninit::as_ptr feature:const_maybe_uninit_as_ptr offset_of->maybe_uninit_as_ptr offset offset feature:const_ptr_offset question_mark using ? in const question_mark->trait_impl mutex_new Mutex::new parking_lot `parking_lot` in `std` mutex_new->parking_lot const_fn_in_patterns const fn callable in patterns const-blocks inline const const_fn_in_patterns->const-blocks from_str FromStr from_str->trait_impl float floats in const fn from_bits to_bits float math, arguments and return types float_classify feature:const_float_classify float_bits_conv feature:const_float_bits_conv float_classify->float_bits_conv float_bits_conv->float const-assert-eq assert_eq! panic_fmt panic! with formatting const-assert-eq->panic_fmt const-assert-eq->trait_impl format_args format_args! panic_fmt->format_args discriminant feature:const_discriminant trait_impl->trait_bound_opt_out raw_ptr_to_usize_cast feature:const_raw_ptr_to_usize_cast raw_ptr_to_usize_cast->unconst_rules extern_const_fn feature:const_extern_fn const_fn_ptr const function pointers const_fn_ptr->trait_bound_opt_out const_fn_ptr->trait_impl format format! format->format_args string String operations format->string format_args->fuzzy-ptr-comparisons format_args->trait_impl vec Vec operations string->vec vec->mut_ref vec->heap vec->raw_ptr_deref vec->trait_impl vec->drop drop->mut_ref drop->trait_impl copy_nonoverlapping ptr::copy_nonoverlapping feature:const_intrinsic_copy copy_nonoverlapping->mut_ref copy_nonoverlapping->raw_ptr_deref async async functions and blocks async->trait_impl