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!

Writing for readers:

14 years of daily writing.

I post practically everything on social media. I authored hundreds of articles, thousands of tweets, and numerous volumes to almost no one.

Tens of thousands of readers regularly praise me.

I despised writing. I'm stuck now.

I've learned what readers like and what doesn't.

Here are some essential guidelines for writing with impact:

Readers won't understand your work if you can't.

Though obvious, this slipped me up. Share your truths.

Stories engage human brains.

Showing the journey of a person from worm to butterfly inspires the human spirit.

Overthinking hinders powerful writing.

The best ideas come from inner understanding in between thoughts.

Avoid writing to find it. Write.

Writing a masterpiece isn't motivating.

Write for five minutes to simplify. Step-by-step, entertaining, easy steps.

Good writing requires a willingness to make mistakes.

So write loads of garbage that you can edit into a good piece.

Courageous writing.

A courageous story will move readers. Personal experience is best.

Go where few dare.

Templates, outlines, and boundaries help.

Limitations enhance writing.

Excellent writing is straightforward and readable, removing all the unnecessary fat.

Use five words instead of nine.

Use ordinary words instead of uncommon ones.

Readers desire relatability.

Too much perfection will turn it off.

Write to solve an issue if you can't think of anything to write.

Instead, read to inspire. Best authors read.

Every tweet, thread, and novel must have a central idea.

What's its point?

This can make writing confusing.

️ Don't direct your reader.

Readers quit reading. Demonstrate, describe, and relate.

Even if no one responds, have fun. If you hate writing it, the reader will too.

Without self-control, you'll waste time chasing dopamine fixes.

I found a powerful quote in Tony Robbins' Awaken The Giant Within:

“Most of the challenges that we have in our personal lives come from a short-term focus” — Tony Robbins

Most people are short-term oriented, but highly successful people are long-term oriented.

Successful people act in line with their long-term goals and values, while the rest are distracted by short-term pleasures and dopamine fixes.

Instant gratification wrecks lives

Instant pleasure is fleeting. Quickly fading effects leave you craving more stimulation.

Before you know it, you're in a cycle of quick fixes. This explains binging on food, social media, and Netflix.

These things cause a dopamine spike, which is entertaining. This dopamine spike crashes quickly, leaving you craving more stimulation.

It's fine to watch TV or play video games occasionally. Problems arise when brain impulses aren't controlled. You waste hours chasing dopamine fixes.

Instant gratification becomes problematic when it interferes with long-term goals, happiness, and life fulfillment.

Most rewarding things require delay

Life's greatest rewards require patience and delayed gratification. They must be earned through patience, consistency, and effort.

Ex:

• A fit, healthy body

• A deep connection with your spouse

• A thriving career/business

• A healthy financial situation

These are some of life's most rewarding things, but they take work and patience. They all require the ability to delay gratification.

To have a healthy bank account, you must save (and invest) a large portion of your monthly income. This means no new tech or clothes.

If you want a fit, healthy body, you must eat better and exercise three times a week. So no fast food and Netflix.

It's a battle between what you want now and what you want most.

Successful people choose what they want most over what they want now. It's a major difference.

Instant vs. delayed gratification

Most people subconsciously prefer instant rewards over future rewards, even if the future rewards are more significant.

We humans aren't logical. Emotions and instincts drive us. So we act against our goals and values.

Fortunately, instant gratification bias can be overridden. This is a modern superpower. Effective methods include:

#1: Train your brain to handle overstimulation

Training your brain to function without constant stimulation is a powerful change. Boredom can lead to long-term rewards.

Unlike impulsive shopping, saving money is boring. Having lots of cash is amazing.

Compared to video games, deep work is boring. A successful online business is rewarding.

Reading books is boring compared to scrolling through funny videos on social media. Knowledge is invaluable.

You can't do these things if your brain is overstimulated. Your impulses will control you. To reduce overstimulation addiction, try:

• Daily meditation (10 minutes is enough)

• Daily study/work for 90 minutes (no distractions allowed)

• First hour of the day without phone, social media, and Netflix

• Nature walks, journaling, reading, sports, etc.

#2: Make Important Activities Less Intimidating

Instant gratification helps us cope with stress. Starting a book or business can be intimidating. Video games and social media offer a quick escape in such situations.

Make intimidating tasks less so. Break them down into small tasks. Start a new business/side-hustle by:

• Get domain name

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Instead of one big mountain, divide it into smaller sub-tasks. This makes a task easier and less intimidating.

#3: Plan ahead for important activities

Distractions will invade unplanned time. Your time is dictated by your impulses, which are usually Netflix, social media, fast food, and video games. It wants quick rewards and dopamine fixes.

Plan your days and be proactive with your time. Studies show that scheduling activities makes you 3x more likely to do them.

To achieve big goals, you must plan. Don't gamble.

Want to get fit? Schedule next week's workouts. Want a side-job? Schedule your work time.