golang interface transfer

Implementation Principles of Types

As a statically typed language, Golang provides a very powerful feature - interface. It not only helps developers achieve code reusability, but also allows us to extend program functionality without destroying the code structure.

In Golang, an interface is a type, but unlike other types, an interface type can contain a set of method declarations without implementing these methods. This gives us great flexibility. By defining an interface type, we can define a general method calling method, and this calling method is associated with the interface type and has nothing to do with the implementation type.

So, when we use the interface type, how does Golang convert it into an implementation type? Before understanding this basic implementation principle, let us first understand the basic concepts of types and interface types in Golang.

Types and interface types in Golang

Types in Golang can be divided into two categories: value types and reference types.

• Value type: numeric type, bool type, array type, structure type, etc.
• Reference types: pointer type, slice type, map type, chan type, etc.

The value type indicates that the variable is stored directly in memory, while the reference type indicates that the variable stores pointers to other objects in memory. For value types, they can be compared directly, while for reference types, the comparison needs to be done using an equivalence function.

In Golang, we can use interface types to represent all types. Interface is a very flexible type because it can represent any type of data value. An interface value can store any data that implements the value of the interface. Therefore, interface types can be used to pass arbitrary types of data to functions or to store object data without knowing the specific object type.

The relationship between types and interface types

In Golang, a type can implement one or more interfaces. A type that implements all methods in an interface is considered an instantiation of the interface. This type can be used as the variable type that implements this interface.

For example, we have an interface type called Shaper, which has a method called Area():

type Shaper interface {

Area() float64

}

We can create a Square type so that it implements the Area() method of the Shaper interface:

type Square struct {

side float64

}

func (s *Square ) Area() float64 {

return s.side * s.side

}

In this way, we can make the Square type an instance of the Shaper type. If we want to calculate the area of ​​the Square type, we can use the Area() method of the Shaper type to obtain the area value:

func main() {

square := &Square{10.0}
fmt.Println("Area of square:", square.Area())

}

Here, we can see that the Square type implements the Area() method of the Shaper type, so it can be used as an instance of the Shaper type. The interface type can provide a general Area() method here to calculate various types of areas, and the implementation of this Area() method is determined by the implementation type.

Why type assertion is needed?

Now that we have understood the basics of types and interface types, let's take a look at how Golang converts interface types into implementation types.

When we create a variable of interface type, it is actually a data structure containing two parts: a pointer to the method table (Method Table, also called a virtual table or Vtable) and a pointer to the implementation Pointer to the value of this interface. The method table is a list of all method function pointers, each pointer is associated with a method name and a type.

When we call a method of an interface type, Golang will first check whether the method is in the method table, and then call the corresponding method. Usually, Golang uses pointer receivers to implement interface types, because this method is more efficient than value receivers and prevents the caller from modifying fields of value types.

But sometimes, when we use an interface type, we need to convert it into an implementation type. At this time, we need to use type assertions. Type assertion is an operation that determines whether type conversion is feasible by judging whether the interface type implements the target type. If the judgment is successful, the type assertion will return a value representing the target type, otherwise it will return a zero value and throw an exception. Therefore, before making type assertions, we need to use the second return value in the type assertion to make safe judgments to prevent exceptions.

The following code shows how to convert an interface type into an implementation type:

func main() {

var shaper Shaper
square := &Square{10.0}
shaper = square                //将square类型转换成Shaper类型
s := shaper.(*Square)          //将shaper类型转换成Square类型
fmt.Println("Square side length:", s.side)

}

Here, By assigning a value of type Square to a variable of type Shaper, we convert the Square type into a Shaper type. When we need to convert it back, we can use type assertion to convert the Shaper type into the Square type.

Summarize

Interface type is a very important concept in Golang, which can improve code reusability and scalability. In Golang, with the help of interface types and type assertions, we can convert interface types into implementation types. Although type assertions bring greater flexibility, you need to pay attention to the safety of type conversion during use to avoid exceptions.

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