pub type Tcl_HashKeyProc = Option<unsafe extern "C" fn(tablePtr: *mut Tcl_HashTable, keyPtr: *mut c_void) -> c_uint>;
pub enum Tcl_HashKeyProc { None, Some(unsafe extern "C" fn(*mut Tcl_HashTable, *mut c_void) -> u32), }
No value.
Some value of type T.
T