What is the use case for Ruby's %q / %Q quoting methods?

Question

I\'ve been reading through Thomas\' Programming Ruby 1.9 and came upon the alternative delimited single and double-quoting methods (%q / %Q). I\'ve known of the

Answer 1

Overview

Apart from "avoid internally escaping quotes" and the examples previously provided by @tadman there are other use-cases as well:

• auto-generating code in the same language as the generator itself (e.g., Ruby generating Ruby)
• providing cleanly-formatted code that does not confuse the syntax-highlighting feature of your text editor
• allow storage of codeblocks that may have to pass through multiple storage layers (such as a database interacting with a website, or a snippets management system interacting with a text editor, which interacts with a subshell, and so forth)

Details

This approach is a general-purpose and robust idiom that works well with any kind of tool that does automated code generation, including but not limited to tools that write boilerplate code in other languages, or tools that manage code snippets for an IDE or text editor.

Besides the examples already provided by @tadman, there is the general case of generating code where the code being generated is the same or substantially similar syntax as the code of the generating program.

In these cases, the solution does a lot more than help with avoiding the use of backslashes to escape quotes. Without a solution like this, there are cases where the generated code can get extremely difficult to maintain.

To see examples of this, feel free to take a look at the following references.

References

[ See e.g.,

• http://en.wikipedia.org/wiki/Leaning_toothpick_syndrome
• http://c2.com/cgi/wiki?QuineProgram
• http://en.wikipedia.org/wiki/Delimiter#Delimiter_collision
• http://en.wikipedia.org/wiki/Quine_(computing)

]