Contract Class Structure

Below restrictions are put in place to simplify code checks during deployment:

• Only 1 inheritance is allowed from ContractBase which is generated by the contract plugin as a nested type in ContractContainer and only 1 inheritance will be allowed from CSharpSmartContract. If there are multiple inheritances from ContractBase or CSharpSmartContract, code deployment will fail.
• Only 1 inheritance will be allowed from ContractState. Similar to above, if there are multiple inheritance from AElf.Sdk.ContractState, code check will fail.
• The type inherited from ContractState should be the element type of CSharpSmartContract generic instance type, otherwise code check will fail.

Contract Class Structure

Limitations on Field Usage

In Contract Implementation Class

• Initial value for non-readonly, non-constant fields is not allowed. (Applied to all static / non-static fields) The reason is, their value will be reset to 0 or null after first execution and their initial value will be lost.

Allowed:

class MyContract : MyContractBase
{
  int test;
  static const int test = 2;
}

Not Allowed:

class MyContract : MyContractBase
{
!  int test = 2;
}

class MyContract : MyContractBase
{
  int test;

  public MyContract
  {
!    test = 2;
  }
}

• Only primitive types, or one of below types are allowed for readonly / constant fields:

Type
All Primitive Types
Marshaller<T>
Method<T, T>
MessageParser<T>
FieldCodec<T>
MapField<T, T>
ReadonlyCollection<T>
ReadonlyDictionary<T, T>

* T can only be primitive type

In Non-Contract Classes (For classes that don’t inherit from ContractBase<T>)

• Initial value for non-readonly, non-constant fields is not allowed for static fields. The reason is, their value will be reset to 0 or null after first execution and their initial value will be lost.

Allowed:

class AnyClass
{
  static int test;
}

Not Allowed:

class AnyClass
{
!  static int test = 2;
}

class AnyClass
{
  static int test;

  public AnyClass
  {
!    test = 2;
  }
}

Exception Case: Fields with FileDescriptor types. This is due to protobuf generated code. There are static fields FileDescriptor type fields generated by protobuf code and these fields don’t have readonly modifier. We allow such fields only if they are FileDescriptor type and write access to these fields are only allowed from the constructor of the type where descriptor field is declared.

Allowed:

public class TestType
{
  private static FileDescriptor test;

  public class TestType
  {
    test = ...
  }
}

Not Allowed:

public class TestType
{
  private static FileDescriptor test;

  public TestType
  {
    test = ...
  }

!  public void SetFromSomeWhereElse(FileDescriptor input)
!  {
!    test = input;
!  }
}

Accessing to set test field is restricted to its declaring type’s constructor only.

• Only below types are allowed for readonly / constant static fields:

Type
All Primitive Types
Marshaller<T>
Method<T, T>
MessageParser<T>
FieldCodec<T>
MapField<T, T>
ReadonlyCollection<T>
ReadonlyDictionary<T, T>

* T can only be primitive type

Exception Case: If a type has a readonly field same type as itself, it is only allowed if the type has no instance field.

This is to support Linq related generated types.

Allowed:

public class TestType
{
  private static readonly TestType test;

  private static int i;
}

Not Allowed:

public class TestType
{
  private static readonly TestType test;

!  private int i;
}

In Contract State

In contract state, only below types are allowed:

Primitive Types
BoolState
Int32State
UInt32State
Int64State
UInt64State
StringState
BytesState

Complex Types
SingletonState<T>
ReadonlyState<T>
MappedState<T, T>
MappedState<T, T, T>
MappedState<T, T, T, T>
MappedState<T, T, T, T, T>
MethodReference<T, T>
ProtobufState<T>
ContractReferenceState