Go_Learning_Fundamental_Allocation

• Reference: effective go

Allocation

Three allocation methods in Go language, new make composite literals; While new and make are build in functions, composite literals is a kind of initialise format. Different allocation method with different feature.

new: build in function, allocate memory , zeros it, ,return the pointer(*T) of type T.

• Apply Type: Any

• Basic Format: new(type)

  • Zeros struct:

    type SyncedBuffer struct {
        lock    sync.Mutex
        buffer  bytes.Buffer
    }
    var p *SyncedBuffer = new(SyncedBuffer) // type *SyncedBuffer
    p := new(SyncedBuffer)  // type *SyncedBuffer

  • Zeros slice:

    var p *[]int = new([]int)       // allocates slice structure; *p == nil; 
    p := new([]int)					//allocates slice structure; *p == nil; 

make:build in function, allocate memory, initialized it, return the value(T) of type T .

• Aapply Type: only slices, maps, channels

• Basic Format: make(type , length , capacity)

  • Initialized Slice:

    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.

    make([]int, 10, 100)

    allocates an array of 100 ints and then creates a slice structure with length 10 and a capacity of 100 pointing at the first 10 elements of the array. When making a slice, the capacity can be omitted;

composite literals: a kind of initialise format, allocate memory, initialized it , return the value(T) of type T

• Apply Type: Any

• Basic Format: Type{value_0, ..., value_n} or Type{item_y : value_x, item_x: value_x, ... }

  • Initialized Slice:

    // TODO: figure out 
    s := []string      {Enone: "no error", Eio: "Eio", Einval: "invalid argument"}

  • Initialized Struct:

    func NewFile(fd int, name string) *File {
        if fd < 0 {
            return nil
        }
        f := File{fd, name, nil, 0}
        return &f
        //  equals to:   return &File{fd, name, nil, 0}
        //  equals to:  return &File{fd: fd, name: name}
    }