在二次开发中，默认的单位为英寸，有时候需要对绘制的线，进行长度统计和单位转换，可通过调用方法进行英寸单位的互转。
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《Head First Ruby》（Jay McGavren）电子书网盘下载免费在线阅读
链接：https://pan.baidu.com/s/1rJdxF4c-rZlArbB8LCVeVg
密码：a7w3书名：Head First Ruby
作者：Jay McGavren
出版社：O'Reilly Media
出版年份：2015-11
页数：576
内容简介：
With Early Release ebooks, you get books in their earliest form—the author's raw and unedited content as he or she writes—so you can take advantage of these technologies long before the official release of these titles. You'll also receive updates when significant changes are made, new chapters as they're written, and the final ebook bundle.
Head First Ruby uses an engaging, active approach to learning that goes beyond dry, abstract explanations and reference manuals. This Head First guide teaches you the Ruby language in a concrete way that gets your neurons zapping and helps you become a Ruby genius. You'll enter at Ruby's language basics and work through progressively advanced Ruby features such as classes, inheritance, and blocks. As your Ruby skills grow, you'll tackle deep topics such as exception handling, modules, and mixins. You'll end by writing your own web app.
作者简介：
Jay McGavren was doing automation for a hotel services company when a colleague introduced him to Programming Perl (a.k.a. the Camel Book). It made him an instant Perl convert, as he liked actually writing code instead of waiting for a 10-person development team to configure a build system. It also gave him the crazy idea to write a technical book someday.
In 2007, with Perl sputtering, Jay was looking for a new interpreted language. With its strong object-orientation, excellent library support, and incredible flexibility, Ruby immediately won him over. He's since used Ruby for two game libraries, a generative art project, in support of a Java development job, and as a Ruby on Rails freelancer. He's been been working in Rails in the online developer education space since 2011
