# Method! and method? **URL:** \ **Category:** Ruby\ **Created:** [September 14, 2010, 4:12pm UTC](https://www.ruby-forum.com/t/method-and-method/194970 "2010-09-14T16:12:37Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![mydarkpassenger](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/82dd89/32.png) [@mydarkpassenger](https://www.ruby-forum.com/u/mydarkpassenger)\ **Post date:** [September 14, 2010, 4:12pm UTC](https://www.ruby-forum.com/t/method-and-method/194970/1 "2010-09-14T16:12:37Z")
I am trying to find the meaning of ! and ? appended to method names but I cannot find what they mean. Can someone explain? ---
**Author:** ![mydarkpassenger](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/82dd89/32.png) [@mydarkpassenger](https://www.ruby-forum.com/u/mydarkpassenger)\ **Post date:** [September 14, 2010, 4:44pm UTC](https://www.ruby-forum.com/t/method-and-method/194970/2 "2010-09-14T16:44:15Z")
Gene A. wrote: > I am trying to find the meaning of ! and ? appended to method names but > I cannot find what they mean. Can someone explain? They don’t mean anything - they are just part of the name. That is, in str.downcase! the method you are calling is called :downcase! - which is a distinct method to :downcase However, there are conventions as to when they should be used. Methods ending ? typically query the properties of some object and return a boolean-like result, while methods ending ! are “dangerous” in some way, such as modifying the state of the object when a non-modifying alternative method is available. ---
**Author:** ![mydarkpassenger](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/82dd89/32.png) [@mydarkpassenger](https://www.ruby-forum.com/u/mydarkpassenger)\ **Post date:** [September 14, 2010, 4:47pm UTC](https://www.ruby-forum.com/t/method-and-method/194970/3 "2010-09-14T16:47:23Z")
On Tue, Sep 14, 2010 at 4:12 PM, Gene A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I am trying to find the meaning of ! and ? appended to method names but > I cannot find what they mean. Can someone explain? From the language functionality point of view, they don’t mean anything. They just happen to be valid characters for method names, and people can use them to give more readability to their code. The core and stdlib classes, though, typically use ! to denote a “dangerous” method. For example a method that modifies the receiver or some side effect. They usually come in pairs with their counterpart having the same name without the !, and usually it means that they both do the same task, but the ! version will modify the receiver. See for example String#gsub and String#gsub!. The ? on the other hand is typically used when the method is a query method, when calling the method would be like asking the object something. Things like Enumerable#include? or Object#equal? Please take note that these are just conventions of method names. You will find destructive or dangerous methods without a !, and query methods without a ?, and possibly the other way around. Jesus. ---
**Author:** ![mydarkpassenger](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/82dd89/32.png) [@mydarkpassenger](https://www.ruby-forum.com/u/mydarkpassenger)\ **Post date:** [September 14, 2010, 4:47pm UTC](https://www.ruby-forum.com/t/method-and-method/194970/4 "2010-09-14T16:47:58Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Tuesday 14 September 2010, Gene A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I am trying to find the meaning of ! and ? appended to method names but > I cannot find what they mean. Can someone explain? First of all, it’s a convention, nothing hard-wired. The question mark is probably the easier to explain: It marks a boolean- returning getter method. Where in e.g. Java you’d write isFile(…) or getStuff(…), with Ruby, it’s just file? or stuff?. The exclamation mark is harder to grasp. It’s meaning is along the lines of “pay attention with this method.” Most commonly it is used to demark a destructive twin of another method. E.g., there can be a #sort and a #sort! method. While the first one would return a sorted copy of the original, the second would modify the original itself. There is, however, no sense in marking every destructive method with an exclamation mark. A File#delete method is obvious enough, there’s no need for a File#delete!. Think of it as the evil twin of the one without the exclamation mark. 🙂 HTH. ``` Eric ``` -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAkyPiJsACgkQhS0drJ3goJIGbQCcDAio4v10CDh5IeFYWW8/Dd2t NgIAnRjtcep7/AY/s3g3xeYvsRuLkloK =IJsL -----END PGP SIGNATURE----- ---
**Author:** ![mydarkpassenger](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/82dd89/32.png) [@mydarkpassenger](https://www.ruby-forum.com/u/mydarkpassenger)\ **Post date:** [September 14, 2010, 5:11pm UTC](https://www.ruby-forum.com/t/method-and-method/194970/5 "2010-09-14T17:11:24Z")
Gene A. wrote: > I am trying to find the meaning of ! and ? appended to method names but > I cannot find what they mean. Can someone explain? They aren’t appended to the method name. They are part of the method name. A method ending in ‘!’ or ‘?’ means pretty much the same as a method name ending in ‘a’ or ‘z’: it means whatever the author of that method wants it to mean. There is a convention, however: a method name ending in ‘?’ usually indicates a method that returns either a truthy or a falsy value. For example, take the `Integer#even?` method. An integer is either even or it’s not. Or `Array#empty?`, `Numeric#zero?`, `Time#thursday?`: an array is either empty or not, a number is either zero or not, a specific date is either a thursday or not. For a method name ending in ‘!’, the convention is the following: if there are two methods that both perform the same operation, but in a slightly different way, then they both get the same name, but the one which is more “surprising” gets an exclamation point appended. For eample: `String#downcase` downcases as string. It returns a new downcased string, but leaves the original untouched. `String#downcase!` _also_ downcases a string, but _it_ destroys the original string and _replaces_ it with a downcased version. jwm ---
**Author:** ![mydarkpassenger](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/82dd89/32.png) [@mydarkpassenger](https://www.ruby-forum.com/u/mydarkpassenger)\ **Post date:** [September 14, 2010, 5:00pm UTC](https://www.ruby-forum.com/t/method-and-method/194970/6 "2010-09-14T17:00:51Z")
This blog post[http://dablog.rubypal.com/2007/8/15/bang-methods-or-danger-will-rubyist](http://dablog.rubypal.com/2007/8/15/bang-methods-or-danger-will-rubyist)has an interesting perspective on the topic.