Struct ffi_type Copy item path

use std::ptr;

#[repr(C)]
struct CustomStruct {
    num: u32,
    num2: i64,
    float_num: f32,
}

// We need to describe the types of the values in `CustomStruct`. The order
// must be the same as the order in the struct definition. Note that this
// array must be alive and at the same address for the entire lifetime of
// the resulting `ffi_type`.
let mut elements_array = unsafe {[
    // `libffi::low::types::uint32`, `sint64`, and `float` can be used
    // instead if using libffi (not -sys)
    ptr::addr_of_mut!(libffi_sys::ffi_type_uint32),
    ptr::addr_of_mut!(libffi_sys::ffi_type_sint64),
    ptr::addr_of_mut!(libffi_sys::ffi_type_float),
    // The last element in the array must be a `NULL` since `ffi_type` does
    // not store the number of elements in the struct.
    ptr::null_mut(),
]};

let mut custom_struct_description = libffi_sys::ffi_type {
    // `libffi::low::type_tag::STRUCT` can be used instead if using libffi
    type_: libffi_sys::FFI_TYPE_STRUCT,
    elements: elements_array.as_mut_ptr(),
    ..Default::default()
};

// `custom_struct_description` can now be used in a [`ffi_cif`] to send
// `CustomStruct` as an argument or receive a `CustomStruct` as response.