ERC165 (or EIP-165) is a standard utilized by various open-source smart contracts like Open Zeppelin or Aavegotchi.

What's it? You must implement? Why do we need it? I'll describe the standard and answer any queries.

What is ERC165

ERC165 detects and publishes smart contract interfaces. Meaning? It standardizes how interfaces are recognized, how to detect if they implement ERC165, and how a contract publishes the interfaces it implements. How does it work?

Why use ERC165? Sometimes it's useful to know which interfaces a contract implements, and which version.

Identifying interfaces

An interface function's selector. This verifies an ABI function. XORing all function selectors defines an interface in this standard. The following code demonstrates.

// SPDX-License-Identifier: UNLICENCED
pragma solidity >=0.8.0 <0.9.0;

interface Solidity101 {
    function hello() external pure;
    function world(int) external pure;
}

contract Selector {
    function calculateSelector() public pure returns (bytes4) {
        Solidity101 i;
        return i.hello.selector ^ i.world.selector;
        // Returns 0xc6be8b58
    }

    function getHelloSelector() public pure returns (bytes4) {
        Solidity101 i;
        return i.hello.selector;
        // Returns 0x19ff1d21
    }

    function getWorldSelector() public pure returns (bytes4) {
        Solidity101 i;
        return i.world.selector;
        // Returns 0xdf419679
    }
}

This code isn't necessary to understand function selectors and how an interface's selector can be determined from the functions it implements.

Run that sample in Remix to see how interface function modifications affect contract function output.

Contracts publish their implemented interfaces.

We can identify interfaces. Now we must disclose the interfaces we're implementing. First, import IERC165 like so.

pragma solidity ^0.4.20;

interface ERC165 {
    /// @notice Query if a contract implements an interface
    /// @param interfaceID The interface identifier, as specified in ERC-165
    /// @dev Interface identification is specified in ERC-165. 
    /// @return `true` if the contract implements `interfaceID` and
    ///  `interfaceID` is not 0xffffffff, `false` otherwise
    function supportsInterface(bytes4 interfaceID) external view returns (bool);
}

We still need to build this interface in our smart contract. ERC721 from OpenZeppelin is a good example.

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC721/ERC721.sol)

pragma solidity ^0.8.0;

import "./IERC721.sol";
import "./extensions/IERC721Metadata.sol";
import "../../utils/introspection/ERC165.sol";
// ...

contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
  // ...

  function supportsInterface(bytes4 interfaceId) public view virtual override(ERC165, IERC165) returns (bool) {
    return
      interfaceId == type(IERC721).interfaceId ||
      interfaceId == type(IERC721Metadata).interfaceId ||
      super.supportsInterface(interfaceId);
  }
  
  // ...
}

I deleted unnecessary code. The smart contract imports ERC165, IERC721 and IERC721Metadata. The is keyword at smart contract declaration implements all three.

Kind (interface).

Note that type(interface).interfaceId returns the same as the interface selector.

We override supportsInterface in the smart contract to return a boolean that checks if interfaceId is the same as one of the implemented contracts.

Super.supportsInterface() calls ERC165 code. Checks if interfaceId is IERC165.

function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
    return interfaceId == type(IERC165).interfaceId;
}

So, if we run supportsInterface with an interfaceId, our contract function returns true if it's implemented and false otherwise. True for IERC721, IERC721Metadata, andIERC165.

Conclusion

I hope this post has helped you understand and use ERC165 and why it's employed.

Have a great day, thanks for reading!

And retire sooner.

Books can make you filthy rich.

If you apply what you learn. In 2011, I was broke and had broken dreams.

Someone suggested I read finance books. One Up On Wall Street was his first recommendation.

Finance books were my crack.

I've read every money book since then. Some are good, but most stink.

These books will make you rich.

The Almanack of Naval Ravikant by Eric Jorgenson

This isn't a cliche book.

This book was inspired by a How to Get Rich tweet thread.

It’s one of the best tweets I’ve ever read.

Naval thinks differently. He nukes ordinary ideas. I've never heard better money advice.

Eric Jorgenson wrote a book about this tweet thread with Navals permission. A must-read, easy-to-digest book.

Best quote

Seek wealth, not money or status. Wealth is having assets that earn while you sleep. Money is how we transfer time and wealth. Status is your place in the social hierarchy — Naval

Morgan Housel's The Psychology of Money

Many finance books advise investing like a dunce.

They almost all peddle the buy an index fund BS. Different book.

It's about money-making psychology. Because any fool can get rich and drunk on their ego. Few can consistently make money.

Each chapter is short. A single-page chapter breaks all book publishing rules.

Best quote

Spending money to show people how much money you have is the fastest way to have less money — Morgan Housel

J.L. Collins' The Simple Path to Wealth

Most of the best money books were written by bloggers.

JL Collins blogs. This easy-to-read book was written for his daughter.

This book popularized the phrase F You Money. With enough money in your bank account and investment portfolio, you can say F You more.

A bad boss is an example. You can leave instead of enduring his wrath.

You can then sit at home and look for another job while financially secure. JL says its mind-freedom is powerful.

Best phrasing

You own the things you own and they in turn own you — J.L. Collins

Tony Robbins' Unshakeable

I like Tony. This book makes me sweaty.

Tony interviews the world's top financiers. He interviews people who rarely do so.

This book taught me all-weather portfolio. It's a way to invest in different asset classes in good, bad, recession, or depression times.

Look at it:

Investing isn’t about buying one big winner — that’s gambling. It’s about investing in a diversified portfolio of assets.

Best phrasing

The best opportunities come in times of maximum pessimism — Tony Robbins

Ben Graham's The Intelligent Investor

This book helped me distinguish between a spectator and an investor.

Spectators are those who shout that crypto, NFTs, or XYZ platform will die.

Tourists. They want attention and to say "I told you so." They make short-term and long-term predictions like fortunetellers. LOL. Idiots.

Benjamin Graham teaches smart investing. You'll buy a long-term asset. To be confident in recessions, use dollar-cost averaging.

Best phrasing

Those who do not remember the past are condemned to repeat it. — Benjamin Graham

The Napoleon Hill book Think and Grow Rich

This classic book introduced positive thinking to modern self-help.

Lazy pessimists can't become rich. No way.

Napoleon said, "Thoughts create reality."

No surprise that he discusses obsession and focus in this book. They are the fastest ways to make more money to invest in time and wealth-protecting assets.

Best phrasing

The starting point of all achievement is DESIRE. Keep this constantly in mind. Weak desire brings weak results, just as a small fire makes a small amount of heat — Napoleon Hill

Ramit Sethi's book I Will Teach You To Be Rich

This book is mostly good.  The part about credit cards is trash.

Avoid credit card temptations. I don't care about their airline points.

This book teaches you to master money basics (that many people mess up) then automate it so your monkey brain doesn't ruin your financial future.

The book includes great negotiation tactics to help you make more money in less time.

Best quote

The 85 Percent Solution: Getting started is more important than becoming an expert — Ramit Sethi

David Bach's The Automatic Millionaire

You've probably met a six- or seven-figure earner who's broke. All their money goes to useless things like cars.

Money isn't as essential as what you do with it. David teaches how to automate your earnings for more money.

Compounding works once investing is automated. So you get rich.

His strategy eliminates luck and (almost) guarantees millionaire status.

Best phrasing

Every time you earn one dollar, make sure to pay yourself first — David Bach

Thomas J. Stanley's The Millionaire Next Door

Thomas defies the definition of rich.

He spends much of the book highlighting millionaire traits he's studied.

Rich people are quiet, so you wouldn't know they're wealthy. They don't earn much money or drive a BMW.

Thomas will give you the math to get started.

Best phrasing

I am not impressed with what people own. But I’m impressed with what they achieve. I’m proud to be a physician. Always strive to be the best in your field…. Don’t chase money. If you are the best in your field, money will find you. — Thomas J. Stanley

by Bill Perkins "Die With Zero"

Let’s end with one last book.

Bill's book angered many people. He says we spend too much time saving for retirement and die rich. That bank money is lost time.

Your grandkids could use the money. When children inherit money, they become lazy, entitled a-holes.

Bill wants us to spend our money on life-enhancing experiences. Stop saving money like monopoly monkeys.

Best phrasing

You should be focusing on maximizing your life enjoyment rather than on maximizing your wealth. Those are two very different goals. Money is just a means to an end: Having money helps you to achieve the more important goal of enjoying your life. But trying to maximize money actually gets in the way of achieving the more important goal — Bill Perkins

Late in 2018, I published my first Medium article, but I didn't start writing seriously until 2019. Since then, I've written more than 240 articles, earned over $50,000 through Medium's Partner Program, and had over 2.5 million page views.

Write A Lot

Most people don't have the patience and persistence for this simple writing secret:

Write + Write + Write = possible success

Writing more improves your skills.

The more articles you publish, the more likely one will go viral.

If you only publish once a month, you have no views. If you publish 10 or 20 articles a month, your success odds increase 10- or 20-fold.

Tim Denning, Ayodeji Awosika, Megan Holstein, and Zulie Rane. Medium is their jam. How are these authors alike? They're productive and consistent. They're prolific.

80% is publishable

Many writers battle perfectionism. 

To succeed as a writer, you must publish often. You'll never publish if you aim for perfection.

Adopt the 80 percent-is-good-enough mindset to publish more. It sounds terrible, but it'll boost your writing success.

Your work won't be perfect. Always improve. Waiting for perfection before publishing will take a long time.

Second, readers are your true critics, not you. What you consider "not perfect" may be life-changing for the reader. Don't let perfectionism hinder the reader.

Don't let perfectionism hinder the reader. ou don't want to publish mediocre articles. When the article is 80% done, publish it. Don't spend hours editing. Realize it. Get feedback. Only this will work.

Make Your Headline Irresistible

We all judge books by their covers, despite the saying. And headlines. Readers, including yourself, judge articles by their titles. We use it to decide if an article is worth reading.

Make your headlines irresistible. Want more article views? Then, whether you like it or not, write an attractive article title.

Many high-quality articles are collecting dust because of dull, vague headlines. It didn't make the reader click.

As a writer, you must do more than produce quality content. You must also make people click on your article. This is a writer's job. How to create irresistible headlines:

Curiosity makes readers click. Here's a tempting example...

• Example: What Women Actually Look For in a Guy, According to a Huge Study by Luba Sigaud

Use Numbers: Click-bait lists. I mean, which article would you click first? ‘Some ways to improve your productivity’ or ’17 ways to improve your productivity.’ Which would I click?

• Example: 9 Uncomfortable Truths You Should Accept Early in Life by Sinem Günel

Most headlines are dull. If you want clicks, get 'sexy'. Buzzword-ify. Invoke emotion. Trendy words.

• Example: 20 Realistic Micro-Habits To Live Better Every Day by Amardeep Parmar

Concise paragraphs

Our culture lacks focus. If your headline gets a click, keep paragraphs short to keep readers' attention.

Some writers use 6–8 lines per paragraph, but I prefer 3–4. Longer paragraphs lose readers' interest.

A writer should help the reader finish an article, in my opinion. I consider it a job requirement. You can't force readers to finish an article, but you can make it 'snackable'

Help readers finish an article with concise paragraphs, interesting subheadings, exciting images, clever formatting, or bold attention grabbers.

Work And Move On

I've learned over the years not to get too attached to my articles. Many writers report a strange phenomenon:

The articles you're most excited about usually bomb, while the ones you're not tend to do well.

This isn't always true, but I've noticed it in my own writing. My hopes for an article usually make it worse. The more objective I am, the better an article does.

Let go of a finished article. 40 or 40,000 views, whatever. Now let the article do its job. Onward. Next story. Start another project.

Disregard Haters

Online content creators will encounter haters, whether on YouTube, Instagram, or Medium. More views equal more haters. Fun, right?

As a web content creator, I learned:

Don't debate haters. Never.

It's a mistake I've made several times. It's tempting to prove haters wrong, but they'll always find a way to be 'right'. Your response is their fuel.

I smile and ignore hateful comments. I'm indifferent. I won't enter a negative environment. I have goals, money, and a life to build. "I'm not paid to argue," Drake once said.

Use Grammarly

Grammarly saves me as a non-native English speaker. You know Grammarly. It shows writing errors and makes article suggestions.

As a writer, you need Grammarly. I have a paid plan, but their free version works. It improved my writing greatly.

Put The Reader First, Not Yourself

Many writers write for themselves. They focus on themselves rather than the reader.

Ask yourself:

This article teaches what? How can they be entertained or educated?

Personal examples and experiences improve writing quality. Don't focus on yourself.

It's not about you, the content creator. Reader-focused. Putting the reader first will change things.

Extreme ownership: Stop blaming others

I remember writing a lot on Medium but not getting many views. I blamed Medium first. Poor algorithm. Poor publishing. All sucked.

Instead of looking at what I could do better, I blamed others.

When you blame others, you lose power. Owning your results gives you power.

As a content creator, you must take full responsibility. Extreme ownership means 100% responsibility for work and results.

You don’t blame others. You don't blame the economy, president, platform, founders, or audience. Instead, you look for ways to improve. Few people can do this.

Blaming is useless. Zero. Taking ownership of your work and results will help you progress. It makes you smarter, better, and stronger.

Instead of blaming others, you'll learn writing, marketing, copywriting, content creation, productivity, and other skills. Game-changer.