05. Composite Types

If the values of a type T can be represented with composite literals, then T{} is its zero value. Справедливо для struct, slice.

Golang	Classic OOP
struct	class with fields, only non-virtual methods
interface	class without fields, only virtual methods
embedding	multiple inheritance AND composition
receiver	implicit this parameter

new expression

Go has two allocation primitives, the built-in functions new and make.

The built-in function new takes a type T, allocates storage for a variable of that type at run time, but unlike its namesakes in some other languages it does not initialize the memory, it only zeros it. That is, new(T) allocates zeroed storage for a new item of type T and returns its address, a value of type *T. In Go terminology, it returns a pointer to a newly allocated zero value of type T.

new(Type) *Type

For instance:

type S struct { a int; b float64 }
new(S)

allocates storage for a variable of type S, initializes it (a=0, b=0.0), and returns a value of type *S containing the address of the location.

make function

The built-in function make(T, args) creates slices, maps, and channels only, and it returns an initialized (not zeroed) value of type T (not *T).

The reason for the distinction between new and make is that these three types represent, under the covers, references to data structures that must be initialized before use. A slice, for example, is a three-item descriptor containing a pointer to the data (inside an array), the length, and the capacity, and until those items are initialized, the slice is nil. For slices, maps, and channels, make initializes the internal data structure and prepares the value for use.

var p *[]int = new([]int)       // allocates slice structure; *p == nil; rarely useful
var v  []int = make([]int, 100) // the slice v now refers to a new array of 100 ints

I found make and new very interesting and hence decided to list down the differences between new and make:

1. new ---> returns pointer make ---> returns an initialized value of type T

2. new ---> initializes to 0 value of the type make ---> does not initialize to 0 value of the type

3. new ---> used for all types make ---> used for only slices, maps and channels