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How to become a Blockchain developer and write your first Smart Contract - Part II

Introduction

Now that you've already learned the basic concepts needed to become a Blockchain developer, in our introductory article, and are more familiar with the entire ecosystem of tools needed, in this article we will see how to write and deploy our first Smart Contract using Solidity.

According to Solidity website:
Solidity is an object-oriented, high-level language for implementing smart contracts. Smart contracts are programs that govern the behavior of accounts within the Ethereum state.

Getting Started with the Solidity language

The easiest way to start writing your first Solidity Smart Contrat is using Remix an online Ethereum IDE.

To start creating your first Smart Contract you need to create a file with the .sol extension. So if you see a file with the .sol extension, that's a Smart Contract.

In Solidity we make use of a preprocessor directive to tell the compiler how to compile our code. Being a statically typed language, all types in our code will be checked in compile time as opposed to runtime. Another difference from other object-oriented languages is that you might be expecting to find the class keyword used to define a new class, but in Solidity we use the keyword contract instead. Since Solidity is influenced by other languages like JavaScript another difference we can notice is the use of the function keyword.

Below is a simple Smart Contract example that we can find in the Solidity website. Let's click on the "open in Remix" button to bring it's content to the Remix IDE so we can start calling some functions on it in order to better undesrtand how it works.

Notice in the image below the use of the .sol extension in the file name and the use of the keyword contract to define a Smart Contract.

How do we call functions in our Smart Contracts?

When you deploy a Smart Contract to an Ethereum network you will get back an address just like your own wallet address. You will then use this address to interact and invoke functions on it.

You will want first to deploy your Smart Contract to a local Blockchain Network using something like Ganache so that you can test your newly created Smart Contract.

Ethereum main public network is called Mainnet, but Ethereum also provide test networks called Testnets that you can use to test your Smart Contracts in a production-like environment.

We have a few icons in the left bar of Remix menu with among other things, options to: 
  1. Create a new workspace in the file explorer
  2. Configure and enable auto compilation
  3. Deploy and call the Smart Contract functions 
  4. Debugger 
  5. Plugin manager  
In the following image we can see we have opened the Solidity Compiler option where we can change the compiler version and toggle auto compilation on/off.
We are going to use the below version for compilation.
To start interacting with our Smart Contract we need to deploy our contract to one of the available environments. We can do that in the "DEPLOY & RUN TRANSACTIONS" section of the IDE. We will use the Remix VM from London as our sandbox running in the browser, as we can see from the image below.
In addition to the Environment option, we have 3 (three) more important configurations to make: the Account Address used to deploy the Smart Contract, the Gas Limit and the Contract which we want to deploy. Once we have all these options configured we can finally go and press the "Deploy" button.

You should be able to see an image similar to the one below showing 2 (two) buttons where we can call the functions in our Smart Contract. This is how we can interact and test our Smart Contract from inside the Remix IDE running in the browser. Since one of our functions expects to receive one parameter so we can set the value of the state variable storedData, the Remix IDE will place an input box right after the function button so we can pass the value to it.
You can see from the logs above, that I have already called the set function. If you open the debug section, in the bottom section of the IDE, you can also check all the information related to this transaction like it's status, transaction hash, block number, the amount of gas used, the transaction cost and the two account addresses involved in this transaction: the smart contract address and the caller address.
Let's now do a small change to our set function by multiplying every passed value by 2 (two) just so we can realize a few things. Click the "Deploy" button to deploy our new version with the change, but before that notice in the following image that we now have another contract, below our first contract, deployed to another address with our change. Also note that we now have 2 (two) versions of our contract deployed at 2 (two) different addresses that we can call functions with different implementations.
Let's now test our new function to see if the value is being multiplied by 2. You can see that we now have the value 80 below our get function button.

Conclusion

In the next article we are going to start using VS Code as our main IDE and the Truffle framework to test and deploy our Smart Contract.

References

Ethereum
Solidity
Ganache
Truffle Framework
MetaMask
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