Question

First of all, I realize I should have tried to fully grasp Ruby before jumping into Rails. However, nothing in Ruby seemed too difficult to quickly grasp (until this!), so I decided to get started while I was still enthusiastic about learning. ,__,

Anyway, here is a super-condensed example of form_for:

<%= form_for(@post) do |f| %>
    <div class="field">
        <%= f.label :name %><br />
        <%= f.text_field :name %>
    </div>
<% end %>

I understand that methods in Ruby need not be called with parenthesis. However, form_for is being called with parenthesis, and yet somehow, it seems as though the do |f| block is being passed to it!

Is form_for returning a method that takes a block, and then is that method immediately being called (without parenthesis) by passing the do |f| block? What’s going on here?

Answer 1

Ruby uses a lot of what is called ‘syntactic sugar’ in that it is a bit more flexible than other languages in how certain operations are interpreted.

for instance:

model.property = "something"

is actually a function call:

model.property=("something")

your form_for example is a similar case. Blocks are silently passed into Ruby functions as a parameter.

my_block = Proc.new { some code }
my_function(param1, param2, &my_block)

is equivalent to

my_function param1, param2 do
  some code
end

and in the function def for my_function you could write:

def my_function(param1, param2, &block)

and you could access the block via the parameter, as well as yield.

So when you use block syntax, it’s interpreted as a parameter, but it’s really not.