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September 26, 2016

Awesome Asciidoctor: Trick To Use Caption Labels And Numbers In References

In Asciidoctor we can add an anchor with an ID to a section or title and then reference it in a link. The title of the section is used as link text. We can alter that when we define the link, but if we rely on the default behaviour we create a title for our section including the caption label and number. This way the created link points to the correct section and the text contains the caption text and number for that section.

In the following example markup we can see how we can use the caption label and section counter as attributes in the title. We do this with the title attribute of a section. By using the single quotes we tell Asciidoctor to interpret the attributes. We must also make sure we set the caption attribute to an empty string value. This disables the default caption creation of Asciidoctor for our section. Finally we need to provide an ID for the section using the #ID syntax:

= Code examples
// Enable the captions for listing blocks.
:listing-caption: Listing

== Creating an application

To create a simple Ratpack application we write
the following code:

// Our listing block has an id of SimpleJavaApp,
// so we can reference it as a link.
// The link text is the title of this listing block.
// We use the listing caption support of Asciidoctor
// in our title with the attributes listing-caption
// and counter:refnum. The value of listing-caption
// is defined with a document attribute (Listing)
// and counter:refnum contains the counter value
// for listing blocks.
// Finally we empty the caption attribute, otherwise
// the default caption rule is used to show Level {counter}.
[#SimpleJavaApp,source,java,caption='',title='{listing-caption} {counter:refnum}. Simple Java Ratpack application']
----
package com.mrhaki;

import ratpack.server.RatpackServer;

public class Main {
    public static void main(String... args) throws Exception {
        RatpackServer.start(server ->
            server
                .handlers(chain ->
                    chain
                        .get(ctx -> ctx.render("Hello World!"))));
    }
}
----

// A second section also with an ID 
// and custom caption and title attributes.
[#SimpleGroovyApp,source,groovy,caption='',title='{listing-caption} {counter:refnum}. Simple Groovy Ratpack application']
----
package com.mrhaki

import static ratpack.groovy.Groovy.ratpack

ratpack {
    handlers {
        get {
            render "Hello World!"
        }
    }
}
----

// In these paragraphs we create a link to the sections with
// id's SimpleJavaApp and SimpleGroovyApp. The text of the links
// will be Listing 1. Simple Java Ratpack application and
// Listing 2. Simple Groovy Ratpack application.
As we can see in <<SimpleJavaApp>> the code is simple. The configuration
of the Ratpack application is done using a series of methods.

With the Groovy code in <<SimpleGroovyApp>> we can use a DSL to define
the application. This results in even better readable code.

When we generate a HTML version of this markup we get the following result:

Written with Asciidoctor 1.5.4.