pub type iv_hashenumproc = Option<unsafe extern "C" fn(name: *mut u8, value: *mut c_void, userdata: *mut c_void) -> i32>;
pub enum iv_hashenumproc { None, Some(unsafe extern "C" fn(*mut u8, *mut c_void, *mut c_void) -> i32), }
No value.
Some value of type T.
T