I joined the 1000 Digital Startups Movement (Gerakan 1000 Startup Digital) in 2017 and learned a lot about the startup sector. My previous essay outlined what a startup is and what must be prepared. Here I'll offer raw ideas for better products.

Intro

A good startup solves a problem. These can include environmental, economic, energy, transportation, logistics, maritime, forestry, livestock, education, tourism, legal, arts and culture, communication, and information challenges. Everything I wrote is simply a basic idea (as inspiration) and requires more mapping and validation. Learn how to construct a startup to maximize launch success.

Adrian Gunadi (Investree Co-Founder) taught me that a Founder or Co-Founder must be willing to be CEO (Chief Everything Officer). Everything is independent, including drafting a proposal, managing finances, and scheduling appointments. The best individuals will come to you if you're the best. It's easier than consulting Andy Zain (Kejora Capital Founder).

Description

To help better understanding from your idea, try to answer this following questions:

- Describe your idea/application
Maximum 1000 characters.

- Background
Explain the reasons that prompted you to realize the idea/application.

- Objective
Explain the expected goals of the creation of the idea/application.

- Solution
A solution that tells your idea can be the right solution for the problem at hand.

- Uniqueness
What makes your idea/app unique?

- Market share
Who are the people who need and are looking for your idea?

- Marketing Ways and Business Models
What is the best way to sell your idea and what is the business model?

Not everything here is a startup idea. It's meant to inspire creativity and new perspectives.

Ideas

#Application

1. Medical students can operate on patients or not. Applications that train prospective doctors to distinguish body organs and their placement are useful. In the advanced stage, the app can be built with numerous approaches so future doctors can practice operating on patients based on their ailments. If they made a mistake, they'd start over. Future doctors will be more assured and make fewer mistakes this way.

2. VR (virtual reality) technology lets people see 3D space from afar. Later, similar technology was utilized to digitally sell properties, so buyers could see the inside and room contents. Every gadget has flaws. It's like a gold mine for robbers. VR can let prospective students see a campus's facilities. This facility can also help hotels promote their products.

3. How can retail entrepreneurs maximize sales? Most popular goods' sales data. By using product and brand/type sales figures, entrepreneurs can avoid overstocking. Walmart computerized their procedures to track products from the manufacturer to the store. As Retail Link products sell out, suppliers can immediately step in.

4. Failing to marry is something to be avoided. But if it had to happen, the loss would be like the proverb “rub salt into the wound”.  On the I do Now I dont website, Americans who don't marry can resell their jewelry to other brides-to-be. If some want to cancel the wedding and receive their down money and dress back, others want a wedding with particular criteria, such as a quick date and the expected building. Create a DP takeover marketplace for both sides.

#Games

1. Like in the movie, players must exit the maze they enter within 3 minutes or the shape will change, requiring them to change their strategy. The maze's transformation time will shorten after a few stages.

2. Treasure hunts involve following clues to uncover hidden goods. Here, numerous sponsors are combined in one boat, and participants can choose a game based on the prizes. Let's say X-mart is a sponsor and provides riddles or puzzles to uncover the prize in their store. After gathering enough points, the player can trade them for a gift utilizing GPS and AR (augmented reality). Players can collaborate to increase their chances of success.

3. Where's Wally? Where’s Wally displays a thick image with several things and various Wally-like characters. We must find the actual Wally, his companions, and the desired object. Make a game with a map where players must find objects for the next level. The player must find 5 artifacts randomly placed in an Egyptian-style mansion, for example. In the room, there are standard tickets, pass tickets, and gold tickets that can be removed for safekeeping, as well as a wall-mounted carpet that can be stored but not searched and turns out to be a flying rug that can be used to cross/jump to a different place. Regular tickets are spread out since they can buy life or stuff. At a higher level, a black ticket can lower your ordinary ticket. Objects can explode, scattering previously acquired stuff. If a player runs out of time, they can exchange a ticket for more.

#TVprogram

1. At the airport there are various visitors who come with different purposes. Asking tourists to live for 1 or 2 days in the city will be intriguing to witness.

2. Many professions exist. Carpenters, cooks, and lawyers must have known about job desks. Does HRD (Human Resource Development) only recruit new employees? Many don't know how to become a CEO, CMO, COO, CFO, or CTO. Showing young people what a Program Officer in an NGO does can help them choose a career.

#StampsCreations

Philatelists know that only the government can issue stamps. I hope stamps are creative so they have more worth.

1. Thermochromic pigments (leuco dyes) are well-known for their distinctive properties. By putting pigments to black and white batik stamps, for example, the black color will be translucent and display the basic color when touched (at a hot temperature).

2. In 2012, Liechtenstein Post published a laser-art Chinese zodiac stamp. Belgium (Bruges Market Square 2012), Taiwan (Swallow Tail Butterfly 2009), etc. Why not make a stencil of the president or king/queen?

3. Each country needs its unique identity, like Taiwan's silk and bamboo stamps. Create from your country's history. Using traditional paper like washi (Japan), hanji (Korea), and daluang/saeh (Indonesia) can introduce a country's culture.

4. Garbage has long been a problem. Bagasse, banana fronds, or corn husks can be used as stamp material.

5. Austria Post published a stamp containing meteor dust in 2006. 2004 meteorite found in Morocco produced the dust. Gibraltar's Rock of Gilbraltar appeared on stamps in 2002. What's so great about your country? East Java is muddy (Lapindo mud). Lapindo mud stamps will be popular. Red sand at Pink Beach, East Nusa Tenggara, could replace the mud.

#PostcardCreations

1. Map postcards are popular because they make searching easier. Combining laser-cut road map patterns with perforated 200-gram paper glued on 400-gram paper as a writing medium. Vision-impaired people can use laser-cut maps.

2. Regional art can be promoted by tucking traditional textiles into postcards.

3. A thin canvas or plain paper on the card's front allows the giver to be creative.

4. What is local crop residue? Cork lids, maize husks, and rice husks can be recycled into postcard materials.

5. Have you seen a dried-flower bookmark? Cover the postcard with mica and add dried flowers. If you're worried about losing the flowers, you can glue them or make a postcard envelope.

6. Wood may be ubiquitous; try a 0.2-mm copper plate engraved with an image and connected to a postcard as a writing medium.

7. Utilized paper pulp can be used to hold eggs, smartphones, and food. Form a smooth paper pulp on the plate with the desired image, the Golden Gate bridge, and paste it on your card.

8. Postcards can promote perfume. When customers rub their hands on the card with the perfume image, they'll smell the aroma.

#Tour #Travel

Tourism activities can be tailored to tourists' interests or needs. Each tourist benefits from tourism's distinct aim.

Let's define tourism's objective and purpose.

• Holiday Tour is a tour that its participants plan and do in order to relax, have fun, and amuse themselves.

• A familiarization tour is a journey designed to help travelers learn more about (survey) locales connected to their line of work.

• An educational tour is one that aims to give visitors knowledge of the field of work they are visiting or an overview of it.

• A scientific field is investigated and knowledge gained as the major goal of a scientific tour.

• A pilgrimage tour is one designed to engage in acts of worship.

• A special mission tour is one that has a specific goal, such a commerce mission or an artistic endeavor.

• A hunting tour is a destination for tourists that plans organized animal hunting that is only allowed by local authorities for entertainment purposes.

Every part of life has tourism potential. Activities include:

1. Those who desire to volunteer can benefit from the humanitarian theme and collaboration with NGOs. This activity's profit isn't huge but consider the environmental impact.

2. Want to escape the city? Meditation travel can help. Beautiful spots around the globe can help people forget their concerns. A certified yoga/meditation teacher can help travelers release bad energy.

3. Any prison visitors? Some prisons, like those for minors under 17, are open to visitors. This type of tourism helps mental convicts reach a brighter future.

4. Who has taken a factory tour/study tour? Outside-of-school study tour (for ordinary people who have finished their studies). Not everyone in school could tour industries, workplaces, or embassies to learn and be inspired. Shoyeido (an incense maker) and Royce (a chocolate maker) offer factory tours in Japan.

5. Develop educational tourism like astronomy and archaeology. Until now, only a few astronomy enthusiasts have promoted astronomy tourism. In Indonesia, archaeology activities focus on site preservation, and to participate, office staff must undertake a series of training (not everyone can take a sabbatical from their routine). Archaeological tourist activities are limited, whether held by history and culture enthusiasts or in regional tours.

6. Have you ever longed to observe a film being made or your favorite musician rehearsing? Such tours can motivate young people to pursue entertainment careers.

7. Pamper your pets to reduce stress. Many pet owners don't have time for walks or treats. These premium services target the wealthy.

8. A quirky idea to provide tours for imaginary couples or things. Some people marry inanimate objects or animals and seek to make their lover happy; others cherish their ashes after death.

#MISCideas

1. Fashion is a lifestyle, thus people often seek fresh materials. Chicken claws, geckos, snake skin casings, mice, bats, and fish skins are also used. Needs some improvement, definitely.

2. As fuel supplies become scarcer, people hunt for other energy sources. Sound is an underutilized renewable energy. The Batechsant technology converts environmental noise into electrical energy, according to study (Battery Technology Of Sound Power Plant). South Korean researchers use Sound-Driven Piezoelectric Nanowire based on Nanogenerators to recharge cell phone batteries. The Batechsant system uses existing noise levels to provide electricity for street lamp lights, aviation, and ships. Using waterfall sound can also energize hard-to-reach locations.

3. A New York Times reporter said IQ doesn't ensure success. Our school system prioritizes IQ above EQ (Emotional Quotient). EQ is a sort of human intelligence that allows a person to perceive and analyze the dynamics of his emotions when interacting with others (and with himself). EQ is suspected of being a bigger source of success than IQ. EQ training can gain greater attention to help people succeed. Prioritize role models from school stakeholders, teachers, and parents to improve children' EQ.

4. Teaching focuses more on theory than practice, so students are less eager to explore and easily forget if they don't pay attention. Has an engineer ever made bricks from arid red soil? Morocco's non-college-educated builders can create weatherproof bricks from red soil without equipment. Can mechanical engineering grads create a water pump to solve water shortages in remote areas? Art graduates can innovate beyond only painting. Artists may create kinetic sculpture by experimenting so much. Young people should understand these sciences so they can be more creative with their potential. These might be extracurricular activities in high school and university.

5. People have been trying to recycle agricultural waste for a long time. Mycelium helps replace light, easily crushed tiles and bricks (a collection of hyphae like in the manufacture of tempe). Waste must contain lignocellulose. In this vein, anti-mainstream painting canvases can be made. The goal is to create the canvas uneven like an amoeba outline, not square or spherical. The resulting canvas is lightweight and needs no frame. Then what? Open source your idea like Precious Plastic to establish a community. By propagating this notion, many knowledgeable people will help improve your product's quality and impact.

6. As technology and humans adapt, fraud increases. Making phony doctor's letters to fool superiors, fake credentials to get hired, fraudulent land certificates to make money, and fake news (hoax). The existence of a Wikimedia can aid the community by comparing bogus and original information.

7. Do you often hit a problem-solving impasse? Since the Doraemon bag hasn't been made, construct an Idea Bank. Everyone can contribute to solving problems here. How do you recruit volunteers? Obviously, a reward is needed. Contributors can become moderators or gain complimentary tickets to TIA (Tech in Asia) conferences. Idea Bank-related concepts: the rise of startups without a solid foundation generates an age as old as corn that does not continue. Those with startup ideas should describe them here so they can be validated by other users. Other users can contribute input if a comparable notion is produced to improve the product or integrate it. Similar-minded users can become Co-Founders.

8. Why not invest in fruit/vegetables, inspired by digital farming? The landowner obtains free fruit without spending much money on maintenance. Investors can get fruits/vegetables in larger quantities, fresher, and cheaper during harvest. Fruits and vegetables are often harmed if delivered too slowly. Rich investors with limited land can invest in teak, agarwood, and other trees. When harvesting, investors might choose raw results or direct wood sales earnings. Teak takes at least 7 years to harvest, therefore long-term wood investments carry the risk of crop failure.

9. Teenagers in distant locations can't count, read, or write. Many factors hinder locals' success. Life's demands force them to work instead of study. Creating a learning playground may attract young people to learning. Make a skatepark at school. Skateboarders must learn in school. Donations buy skateboards.

10. Globally, online taxi-bike is known. By hiring a motorcycle/car online, people no longer bother traveling without a vehicle. What if you wish to cross the island or visit remote areas? Is online boat or helicopter rental possible like online taxi-bike? Such a renting process has been done independently thus far and cannot be done quickly.

11. What do startups need now? A startup or investor consultant. How many startups fail to become Unicorns? Many founders don't know how to manage investor money, therefore they waste it on promotions and other things. Many investors only know how to invest and can't guide a struggling firm.

“In times of crisis, the wise build bridges, while the foolish build barriers.” — T’Challa [Black Panther]

Don't chase cash. Money is a byproduct. Profit-seeking is stressful. Market requirements are opportunities. If you have something to say, please comment.

This is only informational. Before implementing ideas, do further study.

Know why it's important.

The entrepreneur I was meeting with said, "I should be doing crypto, or maybe AI? Aren't those the hot spots? I should look there for a startup idea.”

I shook my head. Yes, they're exciting, but that doesn't mean they're best for you and your business.

“There are different types of entrepreneurs?” he asked.

I said "obviously." Two types, actually. Knowing what type of entrepreneur you are helps you build the right startup.

The two types of businesspeople

The best way for me to describe the two types of entrepreneurs is to start by telling you exactly the kinds of entrepreneurial opportunities I never get excited about: future opportunities.

In the early 1990s, my older brother showed me the World Wide Web and urged me to use it. Unimpressed, I returned to my Super Nintendo.

My roommate tried to get me to join Facebook as a senior in college. I remember thinking, This is dumb. Who'll use it?

In 2011, my best friend tried to convince me to buy bitcoin and I laughed.

Heck, a couple of years ago I had to buy a new car, and I never even considered buying something that didn’t require fossilized dinosaur bones.

I'm no visionary. I don't anticipate the future. I focus on the present.

This tendency makes me a problem-solving entrepreneur. I identify entrepreneurial opportunities by spotting flaws and/or inefficiencies in the world and devising solutions.

There are other ways to find business opportunities. Visionary entrepreneurs also exist. I don't mean visionary in the hyperbolic sense that implies world-changing impact. I mean visionary as an entrepreneur who identifies future technological shifts that will change how people work and live and create new markets.

Problem-solving and visionary entrepreneurs are equally good. But the two approaches to building companies are very different. Knowing the type of entrepreneur you are will help you build a startup that fits your worldview.

What is the distinction?

Let's use some simple hypotheticals to compare problem-solving and visionary entrepreneurship.

Imagine a city office building without nearby restaurants. Those office workers love to eat. Sometimes they'd rather eat out than pack a lunch. As an entrepreneur, you can solve the lack of nearby restaurants. You'd open a restaurant near that office, say a pizza parlor, and get customers because you solved the lack of nearby restaurants. Problem-solving entrepreneurship.

Imagine a new office building in a developing area with no residents or workers. In this scenario, a large office building is coming. The workers will need to eat then. As a visionary entrepreneur, you're excited about the new market and decide to open a pizzeria near the construction to meet demand.

Both possibilities involve the same product. You opened a pizzeria. How you launched that pizza restaurant and what will affect its success are different.

Why is the distinction important?

Let's say you opened a pizzeria near an office. You'll probably get customers. Because people are nearby and demand isn't being met, someone from a nearby building will stop in within the first few days of your pizzeria's grand opening. This makes solving the problem relatively risk-free. You'll get customers unless you're a fool.

The market you're targeting existed before you entered it, so you're not guaranteed success. This means people in that market solved the lack of nearby restaurants. Those office workers are used to bringing their own lunches. Why should your restaurant change their habits? Even when they eat out, they're used to traveling far. They've likely developed pizza preferences.

To be successful with your problem-solving startup, you must convince consumers to change their behavior, which is difficult.

Unlike opening a pizza restaurant near a construction site. Once the building opens, workers won't have many preferences or standardized food-getting practices. Your pizza restaurant can become the incumbent quickly. You'll be the first restaurant in the area, so you'll gain a devoted following that makes your food a routine.

Great, right? It's easier than changing people's behavior. The benefit comes with a risk. Opening a pizza restaurant near a construction site increases future risk. What if builders run out of money? No one moves in? What if the building's occupants are the National Association of Pizza Haters? Then you've opened a pizza restaurant next to pizza haters.

Which kind of businessperson are you?

This isn't to say one type of entrepreneur is better than another. Each type of entrepreneurship requires different skills.

As my simple examples show, a problem-solving entrepreneur must operate in markets with established behaviors and habits. To be successful, you must be able to teach a market a new way of doing things.

Conversely, the challenge of being a visionary entrepreneur is that you have to be good at predicting the future and getting in front of that future before other people.

Both are difficult in different ways. So, smart entrepreneurs don't just chase opportunities. Smart entrepreneurs pursue opportunities that match their skill sets.

Skip this if you don't want to discover why your lively, no-brainer pitch isn't making $10k a month.

You don't want to be repulsive as an entrepreneur or anyone else. Making friends, influencing people, and converting strangers into customers will be difficult if your words evoke disgust, distrust, or disrespect. You may be one of many entrepreneurs who do this obliviously and involuntarily.

I've had to master selling my skills to recruiters (to land 6-figure jobs on Wall Street), selling companies to buyers in M&A transactions, and selling my own companies' products to strangers-turned-customers. I probably committed every cardinal sin of sales repulsion before realizing it was me or my poor salesmanship strategy.

If you're launching a new business, frustrated by low conversion rates, or just curious if you're repelling customers, read on to identify (and avoid) the 6 fatal errors that can kill any sales pitch.

1. The first indication

So many people fumble before they even speak because they assume their role is to convince the buyer. In other words, they expect to pressure, arm-twist, and combat objections until they convert the buyer. Actuality, the approach stinks of disgust, and emotionally-aware buyers would feel "gross" immediately.

Instead of trying to persuade a customer to buy, ask questions that will lead them to do so on their own. When a customer discovers your product or service on their own, they need less outside persuasion. Why not position your offer in a way that leads customers to sell themselves on it?

2. A flawless performance

Are you memorizing a sales script, tweaking video testimonials, and expunging historical blemishes before hitting "publish" on your new campaign? If so, you may be hurting your conversion rate.

Perfection may be a step too far and cause prospects to mistrust your sincerity. Become a great conversationalist to boost your sales. Seriously. Being charismatic is hard without being genuine and showing a little vulnerability.

People like vulnerability, even if it dents your perfect facade. Show the customer's stuttering testimonial. Open up about your or your company's past mistakes (and how you've since improved). Make your sales pitch a two-way conversation. Let the customer talk about themselves to build rapport. Real people sell, not canned scripts and movie-trailer testimonials.

If marketing or sales calls feel like a performance, you may be doing something wrong or leaving money on the table.

3. Your greatest phobia

Three minutes into prospect talks, I'd start sweating. I was talking 100 miles per hour, covering as many bases as possible to avoid the ones I feared. I knew my then-offering was inadequate and my firm had fears I hadn't addressed. So I word-vomited facts, features, and everything else to avoid the customer's concerns.

Do my prospects know I'm insecure? Maybe not, but it added an unnecessary and unhelpful layer of paranoia that kept me stressed, rushed, and on edge instead of connecting with the prospect. Skirting around a company, product, or service's flaws or objections is a poor, temporary, lazy (and cowardly) decision.

How can you project confidence and trust if you're afraid? Before you make another sales call, face your shortcomings, weak points, and objections. Your company won't be everyone's cup of tea, but you should have answers to every question or objection. You should be your business's top spokesperson and defender.

4. The unintentional apologies

Have you ever begged for a sale? I'm going to say no, however you may be unknowingly emitting sorry, inferior, insecure energy.

Young founders, first-time entrepreneurs, and those with severe imposter syndrome may elevate their target customer. This is common when trying to get first customers for obvious reasons.

• Since you're truly new at this, you naturally lack experience.

• You don't have the self-confidence boost of thousands or hundreds of closed deals or satisfied client results to remind you that your good or service is worthwhile.

• Getting those initial few clients seems like the most difficult task, as if doing so will decide the fate of your company as a whole (it probably won't, and you shouldn't actually place that much emphasis on any one transaction).

Customers can smell fear, insecurity, and anxiety just like they can smell B.S. If you believe your product or service improves clients' lives, selling it should feel like a benevolent act of service, not a sleazy money-grab. If you're a sincere entrepreneur, prospects will believe your proposition; if you're apprehensive, they'll notice.

Approach every sale as if you're fine with or without it. This has improved my salesmanship, marketing skills, and mental health. When you put pressure on yourself to close a sale or convince a difficult prospect "or else" (your company will fail, your rent will be late, your electricity will be cut), you emit desperation and lower the quality of your pitch. There's no point.

5. The endless promises

We've all read a million times how to answer or disprove prospects' arguments and add extra incentives to speed or secure the close. Some objections shouldn't be refuted. What if I told you not to offer certain incentives, bonuses, and promises? What if I told you to walk away from some prospects, even if it means losing your sales goal?

If you market to enough people, make enough sales calls, or grow enough companies, you'll encounter prospects who can't be satisfied. These prospects have endless questions, concerns, and requests for more, more, more that you'll never satisfy. These people are a distraction, a resource drain, and a test of your ability to cut losses before they erode your sanity and profit margin.

To appease or convert these insatiably needy, greedy Nellies into customers, you may agree with or acquiesce to every request and demand — even if you can't follow through. Once you overpromise and answer every hole they poke, their trust in you may wane quickly.

Telling a prospect what you can't do takes courage and integrity. If you're honest, upfront, and willing to admit when a product or service isn't right for the customer, you'll gain respect and positive customer experiences. Sometimes honesty is the most refreshing pitch and the deal-closer.

6. No matter what

Have you ever said, "I'll do anything to close this sale"? If so, you've probably already been disqualified. If a prospective customer haggles over a price, requests a discount, or continues to wear you down after you've made three concessions too many, you have a metal hook in your mouth, not them, and it may not end well. Why?

If you're so willing to cut a deal that you cut prices, comp services, extend payment plans, waive fees, etc., you betray your own confidence that your product or service was worth the stated price. They wonder if anyone is paying those prices, if you've ever had a customer (who wasn't a blood relative), and if you're legitimate or worth your rates.

Once a prospect senses that you'll do whatever it takes to get them to buy, their suspicions rise and they wonder why.

• Why are you cutting pricing if something is wrong with you or your service?

• Why are you so desperate for their sale?

• Why aren't more customers waiting in line to pay your pricing, and if they aren't, what on earth are they doing there?

That's what a prospect thinks when you reveal your lack of conviction, desperation, and willingness to give up control. Some prospects will exploit it to drain you dry, while others will be too frightened to buy from you even if you paid them.

Walking down a two-way street. Be casual.

If we track each act of repulsion to an uneasiness, fear, misperception, or impulse, it's evident that these sales and marketing disasters were forced communications. Stiff, imbalanced, divisive, combative, bravado-filled, and desperate. They were unnatural and accepted a power struggle between two sparring, suspicious, unequal warriors, rather than a harmonious oneness of two natural, but opposite parties shaking hands.

Sales should be natural, harmonious. Sales should feel good for both parties, not like one party is having their arm twisted.

You may be doing sales wrong if it feels repulsive, icky, or degrading. If you're thinking cringe-worthy thoughts about yourself, your product, service, or sales pitch, imagine what you're projecting to prospects. Don't make it unpleasant, repulsive, or cringeworthy.

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!