Interfaces in go

Interfaces in go

An interface contains definitions for a group of related functionalities that a non-abstract class or a struct must implement. An interface may define static methods, which must have an implementation.

Part 18: Interfaces - I

Beginning with C 8. An interface may not declare instance data such as fields, auto-implemented properties, or property-like events.

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By using interfaces, you can, for example, include behavior from multiple sources in a class. That capability is important in C because the language doesn't support multiple inheritance of classes. In addition, you must use an interface if you want to simulate inheritance for structs, because they can't actually inherit from another struct or class. You define an interface by using the interface keyword as the following example shows. The name of an interface must be a valid C identifier name.

By convention, interface names begin with a capital I. A class or struct can implement multiple interfaces, but a class can only inherit from a single class. Interfaces can contain instance methods, properties, events, indexers, or any combination of those four member types.

interfaces in go

Interfaces may contain static constructors, fields, constants, or operators. For links to examples, see Related Sections. An interface can't contain instance fields, instance constructors, or finalizers. Interface members are public by default.

To implement an interface member, the corresponding member of the implementing class must be public, non-static, and have the same name and signature as the interface member. When a class or struct implements an interface, the class or struct must provide an implementation for all of the members that the interface declares but doesn't provide a default implementation for. However, if a base class implements an interface, any class that's derived from the base class inherits that implementation.

The implementing class, Carmust provide an implementation of the Equals method.Like a class, an interface can have methods and variables, but the methods declared in an interface are by default abstract only method signature, no body. To declare an interface, use interface keyword. It is used to provide total abstraction. That means all the methods in an interface are declared with an empty body and are public and all fields are public, static and final by default.

A class that implements an interface must implement all the methods declared in the interface. To implement interface use implements keyword. The reason is, abstract classes may contain non-final variables, whereas variables in interface are final, public and static. So we make an interface and put all these common functionalities. And lets Bicycle, Bike, car …. Suppose we need to add a new function in an existing interface.

Obviously the old code will not work as the classes have not implemented those new functions. So with the help of default implementation, we will give a default body for the newly added functions. Then the old codes will still work. New features added in interfaces in JDK 9 From Java 9 onwards, interfaces can contain following also.

This article is contributed by Mehak Kumar. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. Attention reader! Writing code in comment? Please use ide. Interfaces specify what a class must do and not how. It is the blueprint of the class. An Interface is about capabilities like a Player may be an interface and any class implementing Player must be able to or must implement move.Before I started programming Go, I was doing most of my work with Python.

As a Python programmer, I found that learning to use interfaces in Go was extremely difficult. That is, the basics were easy, and I knew how to use the interfaces in the standard library, but it took some practice before I knew how to design my own interfaces.

So what is an interface? An interface is two things: it is a set of methods, but it is also a type. The Speak method takes no arguments and returns a string.

There is no implements keyword in Go; whether or not a type satisfies an interface is determined automatically. We now have four different types of animals: A dog, a cat, a llama, and a Java programmer. In our main function, we can create a slice of Animals, and put one of each type into that slice, and see what each animal says.

Well, no, not really. Since there is no implements keyword, all types implement at least zero methods, and satisfying an interface is done automatically, all types satisfy the empty interface. So, this function:. Wait, what? Within the animals slice, each element is of Animal type, but our different values have different underlying types.

So… why does this matter? Well, understanding how interfaces are represented in memory makes some potentially confusing things very obvious. Not everything is perfect. Another subtlety of interfaces is that an interface definition does not prescribe whether an implementor should implement the interface using a pointer receiver or a value receiver.

In our previous example, we defined all of our methods on value receivers, and we put the associated values into the Animal slice. This error message is a bit confusing at first, to be honest.

interfaces in go

This works because a pointer type can access the methods of its associated value type, but not vice versa. That may sound cryptic, but it makes sense when you remember the following: everything in Go is passed by value. In the case of a method with a value receiver, the value is copied when calling the method.JavaScript seems to be disabled in your browser.

You must have JavaScript enabled in your browser to utilize the functionality of this website. Interfaces allows any user-defined type to satisfy multiple interface types at once. Using Type Assertion you can get a value of a concrete type back and you can call methods on it that are defined on other interface, but aren't part of the interface satisfying.

When a user-defined type implements the set of methods declared by an interface type, values of the user-defined type can be assigned to values of the interface type.

This assignment stores the value of the user-defined type into the interface value. When a method call is made against an interface value, the equivalent method for the stored user-defined value will be executed. Since any user-defined type can implement any interface, method calls against an interface value are polymorphic in nature.

The user-defined type in this relationship is often referred as concrete type.

interfaces in go

Polymorphism is the ability to write code that can take on different behavior through the implementation of types. We have the declaration of a structs named Pentagon, Hexagon, Octagon and Decagon with the implementation of the Geometry interface. The empty interface doesn't have any methods that are required to satisfy it, and so every type satisfies it.

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Defines an interface type named Employee with two methods. Then it defines a type named Emp that satisfies Employee. We define all the methods on Emp that it needs to satisfy Employee.

The Print methods accept a receiver pointer. Hence, the interface must also accept a receiver pointer. If a method accepts a type value, then the interface must receive a type value; if a method has a pointer receiver, then the interface must receive the address of the variable of the respective type.

Interfaces may embed other interfaces, this behavior is an aspect of interface polymorphism which is known as ad hoc polymorphism.


Two or more interfaces can have one or more common method in list of method sets. Here, Structure is a common method between two interfaces Vehicle and Human.

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An Interface is an abstract type. Interface describes all the methods of a method set and provides the signatures for each method.

To create interface use interface keyword, followed by curly braces containing a list of method names, along with any parameters or return values the methods are expected to have.

Pentagon o. Pentagon pent.

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Solutions You Must Read. Most Helpful This Week. Select single argument from all arguments of variadic function. How to use wildcard or a variable in our URL for complex routing? How to find the type of the variable by different ways in Golang?Thus far we have looked at many of the different data types that Go comes with. While you might be able to get away with making any program using only these types; it would be extremely tedious and difficult.

Certain programs reuse data shapes over and over again.

Go - Interfaces

Therefore, creating a custom data type will ultimately save tons of time. In this post, we will be looking at Structs and Interfaces in Go. Structs are basically a custom data type that contains a set of named fields.

In a struct, each field or variable has a type and like with functions we can define multiple fields that share the same type. Consider a Person struct.

Our Person struct contains a name, gender, and age. Above, you can see the different ways that we can use the custom type that we created with this struct. We can access fields later in the code using the dot.

Methods are special functions that we can associate to our structs in Go. We use a special type of syntax to do this. Consider for a moment the creation of a function that prints out our instance of the person struct.

Notice that we are passing the function parameters before the name of the function in this case. This is called using a receiver. The receiver is what allows us to associate this method to the struct Person. It also allows us to call the method with the dot syntax. Go will automatically pass a pointer to this function.

Because the function is associated to our struct of person, we can name it something simple. Lets try creating a different type of struct. In this example, we created a type for a square. We then created a method to calculate the area of the square and then printed that result in our main function. We can also create embedded types using structs.In general programming interfaces are contracts that have a set of functions to be implemented to fulfill that contract.

Go is no different. Go has great support for interfaces and they are implemented in an implicit way. They allow polymorphism in Go. In this post, we will talk about interfaces, what they are, and how they can be used. An interface is an abstract concept which enables polymorphism in Go.

Java Interface Tutorial - Learn Interfaces in Java

A variable of that interface can hold the value that implements the type. Type assertion is used to get the underlying concrete value as we will see in this post. An interface is declared as a type. Here is the declaration that is used to declare an interface. The zero value of an interface is nil. That means it holds no value and type. The code below shows that. An interface is empty if it has no functions at all. An empty interface holds any type. Below is the declaration of an empty interface.

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An interface is implemented when the type has implemented the functions of the interface. Here is an example showing how to implement an interface. Multiple interfaces can be implemented at the same time. If all the functions are all implemented then the type implements all the interfaces. Below the type, the bird type implements both the interfaces by implementing the functions. Interfaces can be composed together.

The composition is one of the most important concepts in software development. When multiple interfaces are implemented then the type has performed composition. This is really helpful where polymorphism is needed.

Type assertion is a way to get the underlying value an interface holds. This means if an interface variable is assigned a string then the underlying value it holds is the string.

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Here is an example showing how to use type assertion using interfaces.An interface in Go is a type defined using a set of method signatures. The interface defines the behavior for similar type of objects. An interface is declared using the type keyword, followed by the name of the interface and the keyword interface. Then, we specify a set of method signatures inside curly braces.

An interface in itself is not that useful unless we use it with a concrete type that implements all its methods. Under the hood, an interface value can be thought of as a tuple consisting of a value and a concrete type:. Checkout the output of the above program and notice how the variable s has information about the value as well as the type of the Shape that is assigned to it. When we call a method on an interface value, a method of the same name on its underlying type is executed.

For example, in the above program, when we call the method Area on the variable sit executes the Area method of its underlying type. How to use interfaces in Go. Liked the Article? Share it on Social media!