Conditional Rendering

Blueprints objects can implement a #render? method, if this method returns false, the blueprint will not be rendered. This allows you extract the conditional logic from component consumer and put in the component itself.

DraftAlert ArticlePage Main Output

class DraftAlert
  include Blueprint::HTML

  def initialize(@article : Article); end

  private def blueprint
    div(class: "alert alert-warning") { "This is a draft" }
  end

  private def render?
    @article.draft?
  end
end

class ArticlePage
  include Blueprint::HTML

  def initialize(@article: Article); end

  private def blueprint
    # Instead of writing:
    # if @article.draft?
    #   render DraftAlert.new(@article)
    # end
    render DraftAlert.new(@article)

    h1 { @article.title }
  end
end

article = Article.new(title: "Hello Blueprint", draft: false)
page = ArticlePage.new(article: article)
page.to_html

<h1>Hello Blueprint</h1>