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This topic is about Solidity – Interfaces.

Interfaces are similar to abstract contracts and are created using interface keyword. Following are the key characteristics of an interface.

• Interface can not have any function with implementation.
• Functions of an interface can be only of type external.
• Interface can not have constructor.
• Interface can not have state variables.
• Interface can have enum, structs which can be accessed using interface name dot notation.

Example

Try the following code to understand how the interface works in Solidity.

pragma solidity ^0.5.0;

interface Calculator {
   function getResult() external view returns(uint);
}
contract Test is Calculator {
   constructor() public {}
   function getResult() external view returns(uint){
      uint a = 1; 
      uint b = 2;
      uint result = a + b;
      return result;
   }
}

Run the above program using steps provided in Solidity First Application chapter.

Note − Select Test from dropdown before clicking the deploy button.

Output

0: uint256: 3

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