do not understand collect method use wit property

Hi all, Can someone explain to me in terms of ruby why this works?

Story.find_all_by_user_id(2).collect(&:link) # 1 method call

This is in ROR console. link is a property of Story. The above command finds all db rows and all their properties (columns) with user_id == 2 and creates an array with only the link property.

This is same as: Story.find_all_by_user_id(2).collect{|x| x.link} # 2 block

I understand function #2 with use of a block.

I do not understand function #1 in terms of syntax. What is &:link? I know it represents a property and could accept that this is the way it works but I want to understand this in terms of ruby syntax. Is &:link a block? If so it would have to represent x.link. I do not understand how this is generated in ruby.

TIA, Pete

They are both equivalent in terms of functionality.

The first is a common rails idiom:

@some_collection.collect(&:id) or @some_collection.map(&:id) #I've seen this one used more than collect...

The ampersand syntax is simply telling the interpreter that the symbol is the block parameter to the method. Internally the to_proc method of the symbol class is called.

Here's a reference: http://apidock.com/rails/Symbol/to_proc

Beware, doing @foo.map(&:id) doesn't perform as well as @foo.map { |f| f.id } for big numbers of foos... Also note that this is a Rails only feature (ie: try it on plain irb and it will not work).

Cool. Thanks for explanation.

Pete

Harold wrote: