Solidity Tutorial: all about interfaces

Hand drawing by Jean Cvllr — different light switches to represent the concept of interfaces

When you flip a light switch, the light goes on.

You do not care “how” the switch turns the light on.

You just care that “it does turn the light on”.

Table of Contents

The idea behind interfaces

What are smart contract interfaces?

Interfaces in Solidity

How to define and use an interface in Solidity?

Functions defined inside an interface.

Function visibility inside interfaces

Benefits of using contract interfaces

Types defined inside an interface

Interfaces and inheritance

Function overloading inside interfaces

Defining events inside interfaces

interfaces and their JSON ABIs

What cannot be defined inside an interface

Security Considerations around interfaces

Useful tools for interfaces

References

The idea behind interfaces

Interfaces are a standard building block and feature of many programming languages. They aim to separate the definition of functionality (a function) from the actual behaviour of the functionality itself.

Let’s use the concept of a light switch mentioned above as an example. Many types of switches (so implementations) exist when you think about it. Here are some examples:

• types of light switches: https://www.electronicshub.org/different-types-of-light-switches/
• or to go a bit further -> types of switches (in general): https://learn.sparkfun.com/tutorials/button-and-switch-basics/all