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This version of the class is more concise and has exactly the same functionality as the longhand version. Now it s time to ask the question: how does attr_accessor work It turns out that attr_accessor isn t as magical as it looks, and it s extremely easy to implement your own version using eval. Consider this code:

FIGURE 7-10 The dark gray Call to Action and medium gray Key Point slides should be the most visually

class Class def add_accessor(accessor_name) self.class_eval %Q{ def #{accessor_name} @#{accessor_name} end def #{accessor_name}=(value) @#{accessor_name} = value end } end end

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The get method is a forgiving way of accessing dictionary items. Ordinarily, when you try to access an item that is not present in the dictionary, things go very wrong:

At first, this code looks complex, but it s very similar to the add_accessor code you created in the previous section. You use class_eval to define getter and setter methods dynamically for the attribute within the current class. If accessor_name is equal to name, then the code that class_eval is executing is equivalent to this code:

The Call to Action headline summarizes the Key Point headlines, and in turn the Key Point headlines summarize the Explanation headlines and the Explanation headlines summarize the Detail slides. Because the Call to Action headline sits at the top of the informational hierarchy, as described in 5, it is really the verbal summary of the entire presentation. Likewise, what you sketch on the Call to Action slide should be a visual summary of the Key Point slides and of the entire presentation if you had only one slide to show, this one would be it. This group of slides formed by the Call to Action and three Key Point slides (CTA+3) is so important, you ll want to sketch the group using the most creative, memorable, and powerful techniques you can come up with. If you have a marketing background, on these slides, you will apply the most powerful branding techniques you know the set of techniques you use to visually distill a message and integrate it through an experience. The only difference here is that you re not applying these techniques to your corporate identity; instead, you re applying them to the highest level of ideas in your presentation. Following are a range of techniques to brand the top level of your thinking on your CTA+3 slides. These sketching ideas are some of the basics as you become comfortable with sketching, try out your own ideas, or invite a graphic designer to give you a hand.

Thus, you have duplicated the functionality of attr_accessor. You can use this technique to create a multitude of different code generators and methods that can act as a macro language to perform things in Ruby that are otherwise lengthy to type out.

Often it s useful to be able to run other programs on the system from your own programs. In this way you can reduce the amount of features your program needs to implement, as you can pass off work to other programs that are already written. It can also be useful to hook up several of your own programs so that functionality is spread among them. Rather than using the Remote Procedure Call systems covered in the previous chapter, you can simply run other programs from your own with one of a few different methods made available by Ruby.

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As long as a comment is on a line by itself, or is the last thing on a line, it s fine. Comment liberally, and your code will be easier to understand.

>>> d = {} >>> print d['name'] Traceback (most recent call last): File "<stdin>", line 1, in KeyError: 'name' Not so with get: >>> print d.get('name') None As you can see, when you use get to access a nonexistent key, there is no exception. Instead, you get the value None. You may supply your own default value, which is then used instead of None: >>> d.get('name', 'N/A') 'N/A' If the key is there, get works like ordinary dictionary lookup: >>> d['name'] = 'Eric' >>> d.get('name') 'Eric'

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