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2.3.4.8.4.4 Abstract/Virtual Methods
Overview
An Abstract Method, or Virtual Method, are methods that are declared but has no underlying implementation (i.e., no body). The primary purpose of these methods is to form a base, template, or guide for subsequent Data Objects derived from this Data Object. The derived Data Objects all have the same behavior defined by the Abstract Methods of the base object. The original base Data Object is considered as Abstract or Virtual since, without implementation for these methods, the Data Object remains a “concept”.
Almost all Object-Oriented Programming (OOP) languages provide for the concept of Abstract or Virtual methods. In recent years, the concept of Virtual or Abstract Data Objects have lost favor to the use of Generics or Templates which can be instantiated for a particular type. For example, a double-linked-lst template, or a name-value pair template.
There are benefits of using Abstract Data Objects1):
| Template | The abstract Data Object enables the best way to execute the process of data abstraction by providing the developers with the option of hiding the code implementation. It also presents the end-user with a template that explains the methods involved. |
| Loose Coupling | Data abstraction in Data Object enables loose coupling, by reducing the dependencies at an exponential level. See 4.3.5.3 System Manageability Issues |
| Code Reusability | Using an abstract Data Object in the code saves time. Abstract Data Objects avoid the process of writing the same code again. |
| Abstraction | Data abstraction in Data Objects helps systems hide code complications and implementation details from Derived Classes (i.e., subclasses) aiding developers of Base Object and Derived Object to focus their attention on an appropriate level. |
DIDO Specifics
Doug Crescenzi 2) does an excellent job in summarizing the use of Abstract Smart Contract and Interfaces.
Ethereum allows for both Interfaces and for Abstract Contracts (i.e., Data Objects). An Abstract Smart Contract is any Smart Contract that has at least one method specified that does not have a corresponding body (implementation). This means that the Abstract Data Object acts like a Base Class, then the Derived Class MUST provide an implementation for the abstract method(s).
pragma solidity ^0.4.24;
contract Person
{ function gender() public returns (bytes32);
}
contract Employee is Person
{ function gender() public returns (bytes32)
{ return "female"; }
}
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