pragmatic-objects / oo-structsubtype

Structural subtyping support for Java interfaces

OO-Structsubtype

Annoation processor that enables declaring Java interfaces with imitation of structural subtyping support

Quick start

1. Add maven dependency:

<dependency>
    <groupId>com.pragmaticobjects.oo.structsubtype</groupId>
    <artifactId>structsubtype-codegen</artifactId>
    <version>x.y.z</version>
</dependency>

2. Declare some interfaces:

interface UserName {
    String userName();
}

interface UserAddress {
    String zip();
    String address();
}

3. Place @StructSubtype declaration to the package-info.java of the package where you want the subtype to be generated

@StructSubtype(name = "User", inherits = { UserName.class, UserAddress.class }
package com.example;

import com.pragmaticobjects.oo.structsubtype.api.StructSubtype;

4. Build the project. A source for new type will be generated at the annotated package. The type will be substitutable at each of it's testators.

interface User extends UserName, UserAddress {}

Note that generated interfaces within one package may be subtypes of each other, if one inherits all features of the other:

@StructSubtype(name = "Recipient", inherits = { UserName.class, UserAddress.class }
@StructSubtype(name = "PassportIdentity", inherits = { UserName.class, PassportId.class }
@StructSubtype(name = "User", inherits = { UserName.class, PassportId.class, UserAddress.class  }
package com.example;

// Since `User` inherits every feature of `Recipient` and `PassportIdentity`, it is considered as a subtype of them.
interface User extends UserName, PassportId, UserAddress, Recipient, PassportIdentity {}