Introducing Code Generation - Picking the Right Mechanism

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To integrate any of these three mechanisms into your code generation process, you’ll separate your application into code you’ll generate and code you’ll write by hand the old way, line by line in an editor. I call the manually written code handcrafted code because it brings to mind the respect I have for handcrafted items. If I build something in my wood shop, I take joy and pride in the crafts I shape by hand. But if I built furniture without power tools, I’d probably never finish, or the quality of the piece would suffer when I rushed. I simply can’t rip5 an 8-foot oak 2×4 efficiently with a handsaw.

Code is the same way. Some jobs are like ripping that long board. Doing them by hand is tedious, demands careful attention to detail, and requires significant skill to maintain the desired consistency. If you decide not to rip the board by hand and create the programmer’s version of a table saw via code generation, you’re creating the right tool for the job. That leaves you more time to focus on parts of the job that aren’t appropriate for the table saw—or creating the parts of your application that aren’t appropriate for code generation.

If you go into a well-stocked building supply store, you’ll see three different categories of table saws. There are entry-level models that are quite easy to get started with because they’re simple to use and require little investment. This is analogous to brute-force code generation. It’s very accessible because the investment in learning new techniques is small, and it’s a good fit for you if you only occasionally use the tool. These tools lack features, but with extra attention you can achieve high-quality output.

The store will also have some large, high-end, and extremely heavy floor models with large fixed out-feed tables. These models are cumbersome and expensive. This is analogous to the CodeDOM. The initial investment is quite large, and the ongoing maintenance is nontrivial. If you’re a full-time cabinetmaker, this might be a good tool, but for the average woodworker, it’s just too much. Similarly, I wouldn’t take on the long-term overhead of CodeDOM unless generating code in multiple languages was my project’s core requirement.

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5. To rip a board means to cut it lengthwise. There’s no doubt that some people can do it with only a manual tool. For example, hopeful miners built hundreds of plank boats from felled trees in a few months along the Yukon Trail. But it isn’t an easy, quick, or fun job!

The store will also have models that lie in the middle. These are the high-quality tabletop models. These have features such as powerful motors and adjustable blades, and they’re built for long-term durability. They’re not only the right tools for anyone with moderate needs, they’re the right tools for anyone needing capacity, portability to job sites, reliability, and ease of use but not wanting a high initial investment or long-term overhead. Similarly, I prefer XSLT for code generation because I think the medium level of initial investment pays off in the long term.

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NOTE Both my shop and my brain tend to be a bit overcrowded. My table saw can also serve as a router table, saving significant space. Similarly, you can reuse skills required for XSLT code generation in working with the XML Document Object Model (DOM) of Visual Studio (which uses XPath). XSLT is also useful for other transformations such as preparing data for HTML display or modifying the format of an XML document.

Each of these table saws performs the same basic tasks. The differences between them would be quite significant as you were selecting a model, but a single book could explain how to build furniture with any of the saws. Similarly, this book covers how to build applications with any of the code generation mechanisms. Unless there are underlying differences between the three, examples in later sections of this book illustrate only XSLT to keep things focused on the core aspects of code generation beyond how you spit out code.

Table 1-1 and Table 1-2 summarize seven potential methods of code generation along with some benefits and drawbacks of each. I’ve included all seven available approaches to put them in perspective and show why only three are viable for your application development and discussed further in this book. Table 1-1 shows the mechanisms I’ll cover in this book, and Table 1-2 shows the mechanisms I won’t discuss further (also discussed in the earlier sidebar “Mechanisms Not Covered”).

XSLT		BRUTE FORCE	CODEDOM
Covered in this book?	Yes	Yes	Yes
Viable for application	Yes	Yes	In some cases
code generation?
Ease of searching	Easy	Difficult	Often impossible
Ease of pasting in	Easy	Difficult	Effectively
sample code			impossible
Multiple language	No	No	Yes
output from one source?
Can generate stored	Yes	Yes	No
procedures?
Restart generation	Continue	Restart	Restart
process for syntax fixes?
VB option statements?	Yes	Yes	Yes, but
			undocumented
Changeable indent width?	Difficult	Yes, with	Yes
		IndentedTextWriter
Regions and vertical	Yes	Yes	To some extent,
whitespace?			but difficult
Other benefits	Relatively easy to	No new language	Code output in
	read your code	or way of thinking	multiple
	while developing	about code	languages
	code generation	required
Drawbacks	Requires learning	Hard to read and	Complex model
	new language	maintain	with tons of
			classes; very hard
			to read

Table 1-2. Four Mechanisms for .NET Code Generation Not Covered

IDE
EXTENSIBILITY				ENTERPRISE
REFLECTION.EMIT		CODEMODEL	VISIO	TEMPLATES
Covered in this book?	No	No	No	No
Viable for application	No	No	No	No
code generation?
Ease of searching	Difficult	Difficult	Impossible	Moderate
Ease of pasting in	Impossible (unless	Difficult	N/A	Moderate
sample code	you paste in MSIL)
Multiple language	No, MSIL only	No	No	No
output from one source?
Can generate stored	No	No	No	No
procedures?
Restart generation	N/A	N/A	N/A	N/A
process for syntax fixes?
VB option statements?	N/A because	N/A	N/A	Yes
	no language-
	specific features
Changeable indent	N/A because no	Yes	No	Yes
width?	source code is
	produced
Regions and vertical	N/A because no	Yes	No	Yes
whitespace?	source code is
	produced
Other benefits	Can be used at	Integrated	Integrates	Unified project
	runtime	into Visual	with UML	starting point;
		Studio IDE	model	allows Informa
				tion Technology
				(IT) control over
				environment
Drawbacks	Code written is	Can’t produce	Only creates	Only creates
	MSIL, not a high-	VB .NET	initial stubs;	initial stubs
	level language; no	output	very hard to
	high-level source		use with VB
	code available		.NET because
	for debugging		of a Visio bug

 

This chapter is from Code Generation in Microsoft .NET by Kathleen Dollard (Apress, 2004, ISBN: 1590591372). Check it out at your favorite bookstore today. Buy this book now.

Next: Breaking Down the Code Generation Process >>
 

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