I am new of Go, and pretty curious of structs. Let's define a struct T
type T struct {
size int
}
I have seen different types of struct initialization. What are the differences?
new(T) // 1
T{size:1} // 2
&T{size:1} // 3
And the two types of method declarations:
func (r *T) area() int // 1
func (r T) area() int // 2
What should be the right way?
new and &T{size:1} returns *T
T{size:1} return T
The built-in function new takes a type T, allocates storage for a variable of that type at run time, and returns a value of type *T pointing to it. The variable is initialized as described in the section on initial values.
2.
The method set of any other named type T consists of all methods with receiver type T. The method set of the corresponding pointer type *T is the set of all methods with receiver *T or T (that is, it also contains the method set of T).
var pt *T
var t T
func (r *T) area() int
you can use pt.area() or t.area()
func (r T) area() int
you can use t.area(), can't use pt.area()
usually we use func(r *T) area() int
Here are different examples:
type Animal struct {
Legs int
Kingdom string
Carnivore bool
}
Initialization by reference
Return the pointer to the struct
var tiger = &Animal{4, "mammalia", true}
fmt.Println(tiger.Kingdom) // print "mammalia"
func changeKingdom(a *Animal) {
a.Kingdom = "alien" // modify original struct
}
changeKingdom(tiger)
fmt.Println(tiger.Kingdom) // print "alien"
Constructor New Initializaiton
Return a pointer with zero-ed values
var xAnimal = New(Animal)
fmt.Println(xAnimal.Kingdom) // print ""
fmt.Println(xAnimal.Legs) // print 0
fmt.Println(xAnimal.carnivore) // print false
changeKingdom(xAnimal)
fmt.Println(xAnimal.Kingdom) // print "alien"
Initialization by value (copy)
Return a separate copy of the original struct
var giraffe = Animal{4, "mammalia", false}
fmt.Println(giraffe.Kingdom) // print "mammalia"
func changeKingdom(a Animal) {
a.Kingdom = "extraterrestrial"
}
changeKingdom(giraffe)
fmt.Println(giraffe) // print "mammalia"
More often you'll deal with pointers when using structs than the copies.