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What's the nature of "property" in a Ruby class?
(3 answers)
Closed 7 years ago.
I have a very basic question about Ruby which I can't seem to answer from browsing online:
property :currency, String
What does 'property' above mean? What circumstances should I use it under?
As for many case in Rails, this is (most probably) a carefully disguised method call. Remember that in Ruby, parenthesis around method calls are options, so:
add(3, 4)
add 3, 4
are equivalent. So in your case,
property :currency, String
can actually be written as:
property(:currency, String)
So, a call to a method called "property" which takes two arguments, a Symbol and a Class. The method is most probably defined on a class from a library you are using.
property :currency, String is a method call. When you find a line like that in a class then that means that a method property is called with :currency and String as parameter.
For the special mean of this method, look at the docs
Related
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What are the restrictions for method names in Ruby?
(5 answers)
Closed 7 years ago.
On the Chef Style Guide page appears this Ruby expression:
antarctica_hint = hint?('antarctica')
What exactly does the ? after hint and before ('antarctica') mean? Is it just part of the method name? (i.e. the method is called 'hint?' not 'hint')
It is part of method name, and people typically (not always) use it for methods that return boolean value.
An example from Ruby is Class#respond_to?
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Why are exclamation marks used in Ruby methods?
(12 answers)
Closed 9 years ago.
Is there a default difference between methods with '!' and without, in ruby?
collect v collect!
flatten v flatten!
and so on..
In ruby the main difference is that, the ! methods are selfish, i.e. they apply the changes to the self object. They return nil, when no changes are done, while the non-! methods create new modified object.
In Rails the difference is that, the ! methods are safe versions of non-! methods, that means the ! methods raises an exception when the code encountered an error during execution, while non-! methods just return error state, usually false condition.
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naked asterisk as parameter in method definition: def f(*)
(1 answer)
Closed 10 years ago.
I was poking through the Rails 3 ActiveRecord source code today and found a method where the entire parameter list was a single asterisk.
def save(*)
I couldn't find a good description of what this does (though I have some ideas based on what I know about splat arguments).
What does it do, and why would you use it?
It means it can have any number of arguments (including zero) and it discards all those arguments.
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What does map(&:name) mean in Ruby?
(17 answers)
Closed 8 years ago.
I saw the code from here
Post.published.collect(&:views_count)
I guess it equals to
.collect { |p| p.views_count }
But I never saw this usage before, does this have a name? Where can I find more information about it?
This is actually a rather clever hack made it into ruby 1.9.
Basically, & in front of a variable in ruby coerces it into a proc. It does that by calling to_proc. Some clever fellow (first time I saw this was in _whys code, but I won't credit him cause I don't know if he came up with it) added a to_proc method to Symbol, that is essentially {|obj| obj.send self}.
There aren't many coercians in ruby, but it seems like all of them are mostly used to do hacks like this (like !! to coerce any type into a boolean)
It's a use of Symbol#to_proc. The & operator turns a Proc object into a block, and because Ruby 1.8.7 and newer implement Symbol#to_proc, it can be used with a symbol like :views_count. And yes, it's equivalent to {|p| p.views_count}.
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What is Ruby's double-colon `::`?
(12 answers)
Closed 8 years ago.
What does :: mean in Ruby? E.g. Foo::Bar.
From the Pickaxe:
When a receiver is explicitly specified in a method invocation, it may be separated from the method name using either a period (.) or two colons (::). The only difference between these two forms occurs if the method name starts with an uppercase letter. In this case, Ruby will assume that a receiver::Thing method call is actually an attempt to access a constant called Thing in the receiver unless the method invocation has a parameter list between parentheses.
It's called a scope resolution operator. Basically a fancy way of referencing a class within a namespace. ActiveRecord is the namespace and Base is the class.
It accesses constants in a given class or module. E.g. ActiveRecord::Base is the constant Base defined in the module ActiveRecord.