When to use blocks

Question

I love Ruby blocks! The idea behind them is just very very neat and convenient.

I have just looked back over my code from the past week or so, which is basically every single ruby function I ever have written, and I have noticed that not a single one of them returns a value! Instead of returning values, I always use a block to pass the data back!

I have even caught myself contemplating writing a little status class which would allow me to write code like :

something.do_stuff do |status|   status.success do      # successful code   end    status.fail do     # fail code     puts status.error_message   end end 

Am I using blocks too much? Is there a time to use blocks and a time to use return values?

Are there any gotchas to be aware of? Will my huge use of blocks come and bite me sometime?

Answer 1

The whole thing would be more readable as:

 if something.do_stuff   #successful code else   #unsuccessful code end 

or to use a common rails idiom:

 if @user.save   render :action=>:show else    @user.errors.each{|attr,msg| logger.info "#{attr} - #{msg}" }    render :action=>:edit end 

IMHO, avoiding the return of a boolean value is overuse of code blocks.

A block makes sense if . . .

It allows code to use a resource without having to close that resource

  open("fname") do |f|   # do stuff with the file  end #don't have to worry about closing the file 

The calling code would have to do non-trivial computation with the result

In this case, you avoid adding the return value to calling scope. This also often makes sense with multiple return values.

 something.do_stuff do |res1, res2|    if res1.foo? and res2.bar?       foo(res1)    elsif res2.bar?       bar(res2)    end  end #didn't add res1/res2 to the calling scope 

Code must be called both before and after the yield

You see this in some of the rails helpers:

  &lt% content_tag :div do  %>      &lt%= content_tag :span "span content" %>   &lt% end -%>  

And of course iterators are a great use case, as they're (considered by ruby-ists to be) prettier than for loops or list comprehensions.

Certainly not an exhaustive list, but I recommend that you don't just use blocks because you can.