Structure of a Contract

Contracts in Viper are contained within files, with each file being one smart-contract. Files in Viper are similar to classes in object-oriented languages. Each file can contain declarations of State Variables, Functions, and structure-structs-types.

State Variables

State variables are values which are permanently stored in contract storage.

storedData: num

See the Types section for valid state variable types and visibility-and-getters for possible choices for visibility.

Functions

Functions are the executable units of code within a contract.

@public
@payable
def bid(): // Function
  // ...
}

function-calls can happen internally or externally and have different levels of visibility (visibility-and-getters) towards other contracts. Functions must be decorated with either @public or @internal.

Events

Events may be logged in specially indexed data structures that allow clients, including light clients, to efficiently search for them.

Payment: __log__({amount: num, arg2: indexed(address)})

total_paid: num

@public
def pay():
    self.total_paid += msg.value
    log.Payment(msg.value, msg.sender)

Events must be declared before global declarations and function definitions.