Reorganize composite type is the base type package, into a special kind of data structure.
contain
Pointer: is the address.
Array: length of the fixed element of the container, not expansion.
Slice: dynamically expansion element container. Array elements can be accessed and sliced according subscript / serial number.
map / map: storage is the key pair. According to access key value. Fast access query speed. To traverse an array or slice need to start from zero.
:: function itself is a data type.
Structure: or Python equivalent java classes.