Rubidity by Example

Let's start with some examples from Solidity's introduction.

Storage Example

This basic Solidity contract sets the value of a variable and then exposes it to others to access:

contract SimpleStorage {
    uint storedData;

    function set(uint x) public {
        storedData = x;
    }

    function get() public view returns (uint) {
        return storedData;
    }
}

Here is how this logic translates to Rubidity:

class Contracts::SimpleStorage < Contract
  uint256 :storedData
  
  function :set, { x: :uint256 }, :public do
    s.storedData = x
  end
  
  function :get, {}, :public, :view, returns: :uint256 do
    return s.storedData
  end
  
  constructor() {}
end

Looking point by point, here's what the Solidity version does and how Rubidity translates it.

Contract Definition

• Solidity: contract SimpleStorage { ... }

• Rubidity: class Contracts::SimpleStorage < Contract

  In Solidity, you define a contract using the contract keyword. In Rubidity, you define a contract as a Ruby class that inherits from a base class called Contract.

State Variable

• Solidity: uint storedData;

• Rubidity: uint256 :storedData

  Solidity uses the uint keyword to define a state variable. Rubidity uses a Ruby symbol to define a state variable along with its type, in this case, uint256.

Function Definitions

Set Function

Solidity:

function set(uint x) public {
  storedData = x;
}

Rubidity:

function :set, { x: :uint256 }, :public do
  s.storedData = x
end

The set function is public in both languages and takes an unsigned integer as an argument. In Rubidity, the function signature also specifies its visibility (:public) and arguments ({ x: :uint256 }).

Get Function

Solidity:

function get() public view returns (uint) {
  return storedData;
}

Rubidity:

function :get, {}, :public, :view, returns: :uint256 do
  return s.storedData
end

The get function is public and has a view property in both languages. The Solidity version uses the returns keyword to specify the return type, while Rubidity does it via the returns: :uint256 option.

Constructor

• Solidity: No explicit constructor.

• Rubidity: constructor() {}

  Both Solidity and Rubidity examples don't utilize a constructor for any initial setup, but the Rubidity code explicitly includes an empty constructor for clarity.

Accessing State

In Rubidity, state variables are accessed using the s. prefix, as seen in s.storedData = x and return s.storedData. Writing to state using an unprefixed variable is not possible in Ruby and the explicitness of s. is nice anyway.

Token Minting Example

Let's break down this OpenMintToken Rubidity contract line-by-line, focusing on how it might translate to a Solidity contract. The contract is an ERC20 token with a capped supply and additional limitations on individual mints.

class Contracts::OpenMintToken < Contract
  is :ERC20
  
  uint256 :public, :maxSupply
  uint256 :public, :perMintLimit
  
  constructor(
    name: :string,
    symbol: :string,
    maxSupply: :uint256,
    perMintLimit: :uint256,
    decimals: :uint256
  ) {
    ERC20(name: name, symbol: symbol, decimals: decimals)
    s.maxSupply = maxSupply
    s.perMintLimit = perMintLimit
  }
  
  function :mint, { amount: :uint256 }, :public do
    require(amount > 0, 'Amount must be positive')
    require(amount <= s.perMintLimit, 'Exceeded mint limit')
    
    require(s.totalSupply + amount <= s.maxSupply, 'Exceeded max supply')
    
    _mint(to: msg.sender, amount: amount)
  end
  
  function :airdrop, { to: :addressOrDumbContract, amount: :uint256 }, :public do
    require(amount > 0, 'Amount must be positive')
    require(amount <= s.perMintLimit, 'Exceeded mint limit')
    
    require(s.totalSupply + amount <= s.maxSupply, 'Exceeded max supply')
    
    _mint(to: to, amount: amount)
  end
end

1. Inheritance: is :ERC20

   • This line means that the OpenMintToken contract inherits from an existing ERC20 contract, inheriting its state variables, functions, and logic.

2. State Variables: uint256 :public, :maxSupply and uint256 :public, :perMintLimit

   • These lines define two public state variables, maxSupply and perMintLimit. Public state variables are accessible to external contracts and can also have getter methods generated automatically.

3. Constructor:

   ruby constructor(
     name: :string,
     symbol: :string,
     maxSupply: :uint256,
     perMintLimit: :uint256,
     decimals: :uint256
   )

   • The constructor function initializes the contract. It takes the token's name, symbol, maximum supply, per-mint limit, and decimals as parameters.

4. State Variable Initialization: s.maxSupply = maxSupply and s.perMintLimit = perMintLimit

   • These lines initialize the state variables using the s. prefix, which is specific to Rubidity for accessing and manipulating state variables.

5. Mint Function:

   function :mint, { amount: :uint256 }, :public do
     require(amount > 0, 'Amount must be positive')
     require(amount <= s.perMintLimit, 'Exceeded mint limit')
     require(s.totalSupply + amount <= s.maxSupply, 'Exceeded max supply')
     _mint(to: msg.sender, amount: amount)
   end

   • This is a public function to mint new tokens. The require statements serve as checks that the amount is positive, within the per-mint limit, and won't exceed the max supply. _mint is a likely internal function inherited from the ERC20 contract that actually mints the tokens.

6. Airdrop Function:

   function :airdrop, { to: :addressOrDumbContract, amount: :uint256 }, :public do
     require(amount > 0, 'Amount must be positive')
     require(amount <= s.perMintLimit, 'Exceeded mint limit')
     require(s.totalSupply + amount <= s.maxSupply, 'Exceeded max supply')
     _mint(to: to, amount: amount)
   end

   • Similar to the mint function but allows specifying a recipient address to. It performs the same require checks and then invokes _mint to create the tokens for the target address.

The Rubidity code uses specific language constructs that mirror Solidity but in a Ruby-like syntax, making it more expressive while maintaining similar logic and functionalities.