notes/pl/groovy/groovy-traits.txt

package devoxx.demo

trait MessageSender {
    void send(String method, Writer writer) {
        writer.print "MESSAGE: $message"
    }
}


import spock.lang.Specification

class MessageSenderSpec extends Specification {
    void 'test @MessageSource annotation adds MessageSender trait to class'() {
        expect:
            MessageSender.isAssignableFrom SomeClass
    }

    void 'test invoking the send method'() {
        given:
            def writer = new StringWriter()
            def obj = new SomeClass()

        when:
            obj.send 'Hi There', writer

        then:
            writer.toString() == 'MESSAGE: Hi There'
    }
}

@MessageSource
class SomeClass {
}


package devoxx.demo

import org.codehaus.groovy.transform.GroovyASTTransformationClass

import java.lang.annotation.Target
import java.lang.annotation.Retention
import java.lang.annotation.RetentionPolicy
import java.lang.annotation.ElementType

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.SOURCE)
@GroovyASTTransformationClass("devoxx.demo.MessagerTransformation")
@interface MessageSource {
}


package devoxx.demo

import org.codehaus.groovy.ast.ASTNode
import org.codehaus.groovy.ast.ClassHelper
import org.codehaus.groovy.ast.ClassNode
import org.codehaus.groovy.ast.CompilePhase
import org.codehaus.groovy.control.SourceUnit
import org.codehaus.groovy.transform.ASTTransformation
import org.codehaus.groovy.transform.GroovyASTTransformation

@GroovyASTTransformation(phase = CompilePhase.SEMANTIC_ANALYSIS)
class MessagerTransformation implements ASTTransformation {
    @Override
    void visit(ASTNode[] nodes, SourceUnit source) {
        ClassNode classNode = nodes[1] // 0 - annotation node, 1 - Foo-class-node

        ClassNode senderNode = ClassHelper.make(MessageSender)

        if (!classNode.declaresInterface(senderNode)) {
            classNode.addInterface(senderNode)
        }
    }
}