Contracts ​

A contract consists of a state together with a single or multiple entrypoints.

It is a class definition that inherits from sp.Contract. The constructor (__init__) makes a call to self.init and initializes fields that make up the contract’s state.

class Hello(sp.Contract):
    def __init__(self):
        self.init(x = 0)

    @sp.entrypoint
    def set_x(newX):
        self.data.x = newX

    @sp.entrypoint
    def check_largerthan_x(p):
        sp.verify(p > self.data.x)

• self.init(..)

  Alias for self.init_storage(arg = None, **kwargs)

• **self.init_storage(arg = None, **kwargs)**

  Set the storage of a contract with no initial storage. arg and kwargs cannot be both present.
  kwargs is a dictionary of fields that are added to the storage (or removed when value is None).

  There are two different ways to call self.init_storage in a contract:

  • on a single value self.init_storage(arg) where arg is a SmartPy expression;
  • on a list of fields with values, self.init_storage(**kwargs) where kwargs is a dictionary.

• **self.update_initial_storage(arg = None, **kwargs)**

  Update the storage of a contract. arg and kwargs cannot be both present. kwargs is a dictionary of fields that are added to the storage (or removed when value is None).

  self.update_initial_storage(e) replaces the former storage while self.update_initial_storage(**kwargs) expects the former storage to be a record and adds, changes or removes (when value is None) former fields. This is very useful when we use complex inheritance patterns.

class Hello(sp.Contract):
    def __init__(self):
        """ Alias for init_storage. """
        self.init(x = 0)

class Hello(sp.Contract):
    def __init__(self):
        """ Initialize the storage to a record containing
            a single field x of value 0. """
        self.init_storage(x = 0)

class Hello(sp.Contract):
    def __init__(self):
        """ It's allowed to call update_initial_storage even if no storage is defined. """
        self.update_initial_storage(x = 0)

class Hello(sp.Contract):
    def __init__(self):
        self.init_storage(x = 0, y = 1)

class Hello(sp.Contract):
    def __init__(self):
        """ Define x then add y. """
        self.init_storage(x = 0)
        self.update_initial_storage(y = 1)

class Hello(sp.Contract):
    def __init__(self):
        """ Define x and t then remove x and add y. """
        self.init_storage(x = 0, t = 12)
        self.update_initial_storage(x = None, y = 1)

Setting storage type ​

class Hello(sp.Contract):
    def __init__(self):
        self.init_type(sp.TRecord(x = sp.TNat))
        self.init(x = 0)

See Setting a type constraint