Solidity for Dummies - Hudson Jameson

you hello everyone the ones who are back from lunch I'm Hudson Jameson I work for the foundation doing DevOps documentation a kind of dap developer just kind of organizing Devcon doing all that stuff so I'm really excited to be here and if you've seen me online my nickname is soup tacular on there and then a piper can do it sure I'm Piper Miriam some of you met me yesterday at the end of the day I maintained a lot of the Python tooling for aetherium I've worked with metallic a bit on proof-of-concept implementations for Casper and just kind of generally theory and developer all right well let's get started we're going to teach you about solidity today so solidity is a high-level language for etherium contracts so what that means is so we don't have to go and do like ones and zeros or like low-level assembly code or things like that we have a high-level language that makes it much easier for humans to be able to code you know at a level they to understand and then put it through the compiler into what will come out and to the etherium network solidity looks a lot like JavaScript but with types it's sort of this interesting amalgamation of of the two this is a very simple solidity contract the highest level thing that we reason about in solidity is the contract object you can think of a contract kind of like a class if you're used to object-oriented programming and the contracts expose some number of functions all right so the code is compiled to the theory and virtual machine y'all probably been hearing about that a lot today pretty much it's just like it takes the human readable code and then puts it into a bunch of Garg legal like ones and zeros and makes it so that the etherium network can read it way that the computer can understand once it's on the EVM it's completely isolated so that's something a lot of people forget but once a contract code is on the etherium network it can't do things like go and you know ping the wthr.com and get the latest weather they have to have a human intermediary because there is isolated there's no outside network or other types of connections and the reason for that isolation is that everything that executes and the EVM has to be completely deterministic which is why you can't generate random numbers easily inside of the EVM it requires some outside interaction contracts are very contracts are very easy to write but they're very difficult to write securely especially if you need to house value or other people's funds this is a pretty straightforward looking function we've gotta withdraw a function for some wallet contract it checks to make sure that there's enough in the account to withdraw it sends the funds that they asked to withdraw and then it sets the balance to what - the new balance this will let somebody completely drain this contract of funds this is exactly what happened to the Dow I have this line underlined because what actually happens here is that this execute can execute code on the address this is sending - and since the account balance is only deducted on the next line that means that that contract can call back into the withdraw method which will execute that line again and it can do this circularly at least until it runs out of gas which means that it can if it can get through a hundred loops of doing this it means it can withdraw a hundred times the amount that it has yep yes this is me public functions let's go over these there callable by anybody so you have this like wallet that has an asset on it and you're you know like I'm gonna make a Hudson coin HUD's coin and you go in there and you're like I want anybody who has access to HUD's coins to be able to check their balance so you make that function public that means anyone can call it as we'll see in a second internal functions are only callable from inside the contract so as you can see there's a lot of parallels to many other programming languages here internal functions are good for you know things that you only want other functions to call so that people can't manipulate them and do weird things with them cool your public functions are the API the expose to the world you can think of these as your API endpoints but they're the things that you allow outside actors to interact with your contract with one of the interesting things is that is happening right now is that some standards are beginning to emerge for how we write contracts you can think of these like HTTP web standards this is the ERC 20 standard this is the standard interface that token contracts enter should implement there's this small set of functions but this interface is implemented across all of the major token contracts that are live on the network right now and that common interface that like standard that has emerged is allowing some pretty awesome things to happen so if anyone's been to the ether scan web site it's a very popular aetherium blockchain Explorer you can go there and they actually have a search feature where if any other contract is using the ERC 20 standard you can search for tokens within that contract it'll you'll just be able to put the contract address and it will tell you you know your balance and give you everything you need because it's a standard that's set across any smart contract that implements it it's very interesting what we have right here is actually maker tokens I believe as because they implemented the ERC 20 interface and there's some variations people use to do different things with ERC 20 but for the most part it's pretty standardized a lot of people are using the same standard which is great that the community can come together and do something like that one of the cool things that these kind of standards enable is this which is a completely decentralized exchange where you can trade token pairs on the etherion blockchain yeah so the cool thing about this like why would we want something like etherics the reason is it doesn't have a middleman it's instant settlement or instant set like pretty close to instant settlement and you control the assets so a lot of the time you forget you know things like this happening and the reason this happened was because it wasn't decentralized they mount GOx was a Bitcoin exchange they had a lot of people's Bitcoin and then they got hacked in the Bitcoin stolen if we were using something like ether X right here that is less likely to happen because the contracts just all talk to each other autonomously within the etherium network let's see oh so solidity is about two years old and since then the communities come together and made a ton of tools you've seen a lot of these today from other presenters and you're going to see more what we have here on the left is some integrated development environment so some of the more popular ones are browser solidity that's a compiler and basically full solidity suite for debugging and everything within your browser we also have a theorem studio and Visual Studio which are IDs and plugins and then if you look at the bottom if you recognize any of those assembly that means that your text editor has support for solidity syntax or solidity compilation or things like that if you look at the right we have tools rain earlier today when Oversoul graph which is a really really powerful tool we also have a selenium which is a linter truffled apple populist and embark which are frameworks for building dabs so really you have a ton of different tools to come in and help you learn because it can be a rough ride at first so yeah go ahead so this is browser solidity this is magic you can go to this in your browser right now if you can get the internet to work and write a contract compile it here in your browser without any tooling on your machine deploy it to a testy VM running in your browser without you needing to install anything on your machine and interact with it right here on this website the browser solidity is an amazing amazing tool and it is a really easy way to get started tinkering around with etherium contracts yeah definitely so I was gonna put a list of resources like okay I'm out there in the audience or watching online I want to get started what do I do what we've done is if you go to the etherium subreddit it's like an online forum there's a post that's at the top of the homepage of the etherium subreddit and it has all kinds of links it has a getting started guide some of the things that people are going to be familiar with and that are real easy to use we have our own Stack Exchange so if you're a developer with different languages and you use Stack Exchange aetherium has its own Stack Exchange that actually has over 3000 at least 3,500 questions answered we also have ethics org which is a community built documentation site we're looking all the time for people to come in help out with that effort and we also have a course aetherium org which has a short getting started and then on top of that we have plans in the future to expand on may be things like examples tutorials and then of course for solidity there is a solidity documentation that is constantly updated with every release so it's very very good resource on top of all that you're in there it's going to be kind of hectic at first if you've never used solidity there's a little bit of a learning curve so come to our git er chat rooms and that's going to be I think git er dot i n slash aetherium we have developers and different channels there at all times that'll be happy to help you get started with aetherium so I think with that the only other thing I have to remind you guys go ahead and talk about you um so I've signed up about 10% of the conference for DEFCON 2 identities I'd love to get a much deeper signup so send me your information I don't know if we can get the slide yeah it's like it come up but I will say this if you walked out early yesterday you missed the most amazing announcement because what we have here is a memento on the etherion blockchain that you can pull up or you can so so I am issuing one one of these to every person here that wants one they won't be issuable after Thursday morning at 8:00 a.m. and the idea is this is an experiment to see what can we do with the ability to let people interact with something knowing that they were here at this conference there are some interesting ideas that I have for what you could build on top of this one of them might be if there's another hard fort proposal at some point we could use this as the permissions for voting in one vote to see what this community thinks about that idea as opposed to the entire community of people who own ether might be interesting to see what the difference between those two boats are that is oddly interesting yeah all you have to do is send me your information yeah Piper's camped out like outside at a desk with some stickers and if you come over there with your aetherium address you'll be in a once-in-a-lifetime opportunity smart contract to be able to provide you know your input and future events potentially so super exciting stuff I'm really excited about solidity if you need any help with it find me on reddit my name is supe tacular on there it's a great name it's my yeah and then Piper's on there as a hyper Miriam hyper Miriam find him on there - he's super helpful where nice guys come see us thank you