In Ruby, a standard convention is to use a question mark at the end of a method name to indicate the method returns a boolean result:
[].empty? #=> true
Another standard convention is to end a method name with an exclamation point if the method is destructive (that is, it modifies the original data):
mylist.sort! # sort mylist in-place
Recently I have seen these same conventions used in Scheme. Which makes me wonder, what other languages use/support this convention? Are there any other special characters that are commonly used for naming by these or other languages?
The answer is, of course, language (and language culture) specific.
For example, depending on the language, all of the following are appropriate: empty-p, empty?, empty, is_empty or isEmpty. (These examples are, of course, not inclusive).
The examples in the original question come from Ruby where such use of ? and ! to end method names are, where appropriate, accepted. This acceptance comes from 1) readily accessible as symbol terminators in the grammar 2) use of ? and ! in the standard library. However, it should be note that ! is not used universally to imply "side-effect" and is generally only present on alternative forms: save/save!, sort/sort!, etc. There are an overwhelming number of methods that perform side-effects which do not have the ! prefix.
Personally, if I was designing a language, I would allow ?, ! and ' to be valid unquoted trailing characters in symbol names. Even though that some languages allow full symbol escaping, such as Scala, such symbols are usually avoided because it's a pain to have to quote them for use.
// in Scala, esp. with Java-compat, the last form is generally used although
// the first two are perfectly valid -- do what makes sense in the language
foo.`empty?`
foo.empty_?
foo.isEmpty
When in Rome...
empty? or empty_? (not common)if not len(foo): "empty!")Glad to see corrections and/or additions -- is only a drop in a bucket.