Interfaces and inheritance basics

Shared declarations and inherited implementation have different jobs.

LET’S PICTURE IT

A plug specification says how to connect; inheriting a component can bring its actual machinery too.

SEE IT FOR YOURSELF

A valid counter call, step by stepStep 1 / 4

This example begins with count zero and a request to call increment(). No real contract is deployed.

Animated local teaching model. No wallet, RPC or live blockchain data. Some labels and hashes are abbreviated for readability.

An interface describes callable shapes

Solidity interfaces declare expected external behavior without providing the ordinary implementation body for those functions. They help code call a contract through an agreed type.

Inheritance can bring code and state

A derived contract can inherit behavior and variables from bases. The effective permissions and storage layout can therefore depend on declarations outside the visible derived file.

Overrides need inspection

Language rules determine how overrides are declared and selected. A familiar base name does not prove that a derived override preserves every safety property.

The deployed address still matters

Casting an address to an interface does not prove matching code is deployed there. It tells the compiler how to encode calls, leaving runtime behavior and network identity as separate evidence.

Read the example

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

interface ICounter {
    function count() external view returns (uint256);
}

contract LearningExample {
    function read(ICounter target) external view returns (uint256) {
        return target.count();
    }
}

The target address must actually provide compatible behavior for the call to succeed.

QUICK CHECK · NO PRESSURE

Does casting an address to an interface authenticate the code at that address?

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