# Conditional modifier syntax

**URL:** <https://www.ruby-forum.com/t/conditional-modifier-syntax/73140>\
**Category:** Ruby\
**Created:** [October 21, 2006, 11:28pm UTC](https://www.ruby-forum.com/t/conditional-modifier-syntax/73140 "2006-10-21T23:28:35Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Pau\_Garcia\_i\_Quiles](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/b9e5f3/32.png) [@Pau\_Garcia\_i\_Quiles](https://www.ruby-forum.com/u/Pau_Garcia_i_Quiles)\
**Post date:** [October 21, 2006, 11:28pm UTC](https://www.ruby-forum.com/t/conditional-modifier-syntax/73140/1 "2006-10-21T23:28:35Z")

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Hello,

Am I the only one who finds beautiful this syntax for conditional  
modifiers?

@playlist= source[:playlist] if  
source[:playlist].instance\_of?(XSPF::Playlist)  
else raise TypeError “The playlist must be an instance of  
XSPF::Playlist”

It reads like a book even if you don’t know Ruby: “@playlist is X if  
this or Y  
if not”

PS: It’s beautiful but it doesn’t work :-/

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**Author:** ![Pau\_Garcia\_i\_Quiles](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/b9e5f3/32.png) [@Pau\_Garcia\_i\_Quiles](https://www.ruby-forum.com/u/Pau_Garcia_i_Quiles)\
**Post date:** [October 21, 2006, 11:34pm UTC](https://www.ruby-forum.com/t/conditional-modifier-syntax/73140/2 "2006-10-21T23:34:40Z")

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Pau Garcia i Quiles wrote:

> Hello,
> 
> Am I the only one who finds beautiful this syntax for conditional modifiers?
> 
> @playlist= source[:playlist] if source[:playlist].instance\_of?(XSPF::Playlist)  
> else raise TypeError “The playlist must be an instance of XSPF::Playlist”
> 
> PS: It’s beautiful but it doesn’t work :-/

Well, you can use if in two different ways:

a if b

or

if a  
b  
end

Only in the second case you can use else. I would write it this way:  
(in two lines, in case that doesn’t show in the mail)

raise TypeError “The playlist must be an instance of XSPF::Playlist”  
unless source[:playlist].instance\_of?(XSPF::Playlist)  
@playlist= source[:playlist]

I tend to find that more clear: you first leave out the case that  
doesn’t interest you.

Just my opinion 😉 !

```
Vince
```

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<div class="post-metadata">

**Author:** ![Pau\_Garcia\_i\_Quiles](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/b9e5f3/32.png) [@Pau\_Garcia\_i\_Quiles](https://www.ruby-forum.com/u/Pau_Garcia_i_Quiles)\
**Post date:** [October 23, 2006, 2:13am UTC](https://www.ruby-forum.com/t/conditional-modifier-syntax/73140/3 "2006-10-23T02:13:47Z")

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Pau Garcia i Quiles wrote:

> PS: It’s beautiful but it doesn’t work :-/

I wouldn’t like else in conditional modifiers for the same reason I  
don’t like conditional modifiers after code blocks (the not-a-closure  
kind).

I prefer to use them for trivial special case handling (early returns,  
loop cycle breaks) when it’s more important to see what’s happening than  
why. (I find it easier to visually parse past a block of “return nil if  
some\_condition” on the beginning of a method to get to the main logic,  
for example.)

A conditional modifier effectively “hides” the conditional; when used  
with a code block, it’s cheating people reading your code into believing  
there’s one level of logic flow nesting less (it’s not immediately  
visible as indentation, for example). There’s a word for this:  
obfuscation.

The above code snippet also doesn’t read as you describe it, instead it  
reads “@playlist is X if X is a Playlist, fail if not.” You place the  
failure in the source after the assignment, when in fact you’re checking  
against a precondition. (Emphasis on pre-). The method fails -before-  
the assignment, placing the cause of the failure after it is misleading.

I’d rewrite the code snippet as:

raise TypeError “The playlist must be an instance of XSPF::Playlist”  
unless source[:playlist].is\_a? XSPF::Playlist

@playlist = source[:playlist]

grouping the special cases (precondition checking) at the beginning of  
the method to ensure that any failure of those is clean and doesn’t  
leave the object in an inconsistent state.

David V.