What do these weird characters mean?

Question

I'm reading a Ruby book but it doesn't explain the following:

1. What is this: validates :name, :presence => true

   • I mean I know what it does but what's validates? Is it a method of the validator class? If so, how come it's called without mentioning the class name first?

   • What's the meaning of : in the previous code and in Rails on general?

2. In the following code: <%= form_for([@post, @post.comments.build]) do |f| %>

   • Is form_for an object or a procedural function?

   • What's the meaning of the | character in |f|

3. In <%= link_to 'Edit Post', edit_post_path(@post) %>

   • Who, where and when was edit_post_path method defined?

   • To which class it belongs?

Answer 1

1. validates is a method, part of the validators in Rails. It is declared in (actually, included to) a superclass, that is why it does not have to be declared in the model. The : in front of anything signifies a symbol, not a variable. Symbols are part of Ruby, somewhat similar to strings.
2. form_for is a method, which takes a number of parameters and a block (that is why there is a do afterwards). The | is part of Ruby syntax, the way you enclose code block parameters.
3. edit_post_path is defined by the Rails magic and the routes. It is a helper method.

I encourage you to read this book about Ruby to get more familiar with symbols, code blocks, modules and other things that make Ruby a great programming language.