Does go language have constructors?

Go language has no constructor. Go language, as a structured language, does not have constructors in object-oriented languages. However, similar effects of constructors in object-oriented languages ​​can be achieved in some ways, that is, using the process of structure initialization to simulate the implementation of constructors.

The operating environment of this tutorial: Windows 7 system, GO version 1.18, Dell G3 computer.

The constructor is a special method, mainly used to initialize the object when creating the object, that is, assign initial values ​​to the object member variables. A special class can have multiple constructors, which can be distinguished according to the number of parameters or the types of parameters, that is, the overloading of constructors.

As a structured language, Golang does not have the constructor methods in object-oriented languages, but Golang can implement object-oriented programming ideas and methods like inheritance and constructors like C.

Because struct is a value type, if the structure is more complex, the value copy performance overhead will be relatively large, so the constructor returns the structure Body pointer type.

Specification

• Start with New keyword

• Return structure pointer

Multiple ways to create and initialize structures - simulate constructor overloading

If you use a structure to describe the characteristics of a cat, then There can be different types of cats according to their colors and names. Then different colors and names are fields of the structure. At the same time, you can use colors and names to construct instances of different types of cats. For this process, you can refer to the following code:

type Cat struct {
    Color string
    Name  string
}
func NewCatByName(name string) *Cat {
    return &Cat{
        Name: name,
    }
}
func NewCatByColor(color string) *Cat {
    return &Cat{
        Color: color,
    }
}

The code description is as follows:

• Line 1 defines the Cat structure, including color and name fields.

• Line 6 defines a function that constructs a cat structure by name and returns a Cat pointer.

• Line 7 takes the address and instantiates the cat structure.

• Line 8 initializes the cat’s name field and ignores the color field.

• Line 12 defines a function that constructs a cat structure with color and returns a Cat pointer.

In this example, the types of the two attributes, color and name, are both strings. Since there is no function overloading in the Go language, in order to avoid function name conflicts, use NewCatByName() and NewCatByColor() Two different function names represent different Cat construction processes.

Construction and initialization of structures with parent-child relationships - simulating parent construction calls

The black cat is a kind of cat, cat It is a general term for black cat. When describing these two concepts at the same time, it is derived. Black cat is derived from the type of cat. When using a structure to describe the relationship between cat and black cat, the structure of cat is embedded in black cat. In cat (BlackCat), it means that black cat has the characteristics of cat, and then uses two different constructors to construct two structure instances of black cat and cat respectively. Refer to the following code:

type Cat struct {
    Color string
    Name  string
}
type BlackCat struct {
    Cat  // 嵌入Cat, 类似于派生
}
// “构造基类”
func NewCat(name string) *Cat {
    return &Cat{
        Name: name,
    }
}
// “构造子类”
func NewBlackCat(color string) *BlackCat {
    cat := &BlackCat{}
    cat.Color = color
    return cat
}

Code description As follows:

• Line 6 defines the BlackCat structure and embeds the Cat structure. BlackCat owns all members of Cat and can freely access all members of Cat after instantiation.

• In line 11, the NewCat() function defines the construction process of Cat, using the name as a parameter to fill in the Cat structure.

• Line 18, NewBlackCat() uses color as a parameter and constructs a BlackCat pointer.

• Line 19, instantiate the BlackCat structure, and Cat is also instantiated at the same time.

• Line 20, fill in the Cat color attribute embedded in BlackCat. BlackCat does not have any members, and all members come from Cat.

In this example, the Cat structure is similar to the "base class" in object-oriented, and BlackCat is embedded in the Cat structure, which is similar to the "derivative" in object-oriented. When instantiated, The Cat in BlackCat will also be instantiated.

In short, the Go language does not provide a special mechanism related to constructors. Users can complete the task of the constructor by passing the parameters into the structure construction parameters according to their own needs.

【Related recommendations: Go video tutorial, Programming teaching】

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