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# good
date = `date`
echo = %x(echo `date`)
----
=== `%s` [[percent-s]]
Avoid the use of `%s`.
It seems that the community has decided `:"some string"` is the preferred way to create a symbol with spaces in it.
=== Percent Literal Braces [[percent-literal-braces]]
Use the braces that are the most appropriate for the various kinds of percent literals.
* `()` for string literals (`%q`, `%Q`).
* `[]` for array literals (`%w`, `%i`, `%W`, `%I`) as it is aligned with the standard array literals.
* `{}` for regexp literals (`%r`) since parentheses often appear inside regular expressions. That's why a less common character with `{` is usually the best delimiter for `%r` literals.
* `()` for all other literals (e.g. `%s`, `%x`)
[source,ruby]
----
# bad
%q{"Test's king!", John said.}
# good
%q("Test's king!", John said.)
# bad
%w(one two three)
%i(one two three)
# good
%w[one two three]
%i[one two three]
# bad
%r((\w+)-(\d+))
%r{\w{1,2}\d{2,5}}
# good
%r{(\w+)-(\d+)}
%r|\w{1,2}\d{2,5}|
----
== Metaprogramming
=== No Needless Metaprogramming [[no-needless-metaprogramming]]
Avoid needless metaprogramming.
=== No Monkey Patching [[no-monkey-patching]]
Do not mess around in core classes when writing libraries (do not monkey-patch them).
=== Block `class_eval` [[block-class-eval]]
The block form of `class_eval` is preferable to the string-interpolated form.
==== Supply Location [[class-eval-supply-location]]
When you use the string-interpolated form, always supply `+__FILE__+` and `+__LINE__+`, so that your backtraces make sense:
[source,ruby]
----
class_eval 'def use_relative_model_naming?; true; end', __FILE__, __LINE__
----
==== `define_method` [[class-eval-define_method]]
`define_method` is preferable to `class_eval { def ... }`
=== `eval` Comment Docs [[eval-comment-docs]]
When using `class_eval` (or other `eval`) with string interpolation, add a comment block showing its appearance if interpolated (a practice used in Rails code):
[source,ruby]
----
# from activesupport/lib/active_support/core_ext/string/output_safety.rb
UNSAFE_STRING_METHODS.each do |unsafe_method|
if 'String'.respond_to?(unsafe_method)
class_eval <<-EOT, __FILE__, __LINE__ + 1
def #{unsafe_method}(*params, &block) # def capitalize(*params, &block)
to_str.#{unsafe_method}(*params, &block) # to_str.capitalize(*params, &block)
end # end
def #{unsafe_method}!(*params) # def capitalize!(*params)
@dirty = true # @dirty = true
super # super
end # end
EOT
end
end
----
=== No `method_missing` [[no-method-missing]]
Avoid using `method_missing` for metaprogramming because backtraces become messy, the behavior is not listed in `#methods`, and misspelled method calls might silently work, e.g. `nukes.luanch_state = false`.
Consider using delegation, proxy, or `define_method` instead.
If you must use `method_missing`: