What's this &block in Ruby? And how does it get passed in a method here? -

Look at this piece of code on Ruby on Rail Book This first scene is from one scene and the other one is the assistant module. I do not understand how this and block and attributes = {} work can someone guide me in some kind of tutorial like this?

  & lt;% hidden_div_if (@ cart.items.empty ?,, id = & gt; "cart") What is% & gt; & Lt;% = Render (: partial = & gt; "cart",: object = & gt; @ cart)%> & Lt;% end% & gt; If the condition properties ["style"] = "display: none" end content_tag ("div", attributes, and block) end of the module storehalers df hiding_vi_if (position, attributes = {}, and block)  < / Pre> 

The blocks are a fairly basic part of Ruby, they are either do. Arg0, arg1 | Are separated by ... end or {| Arg0, arg1, arg2 | ...} .

They allow to specify a callback to pass some method. This callback can be implemented in two ways - by either specifying the last logic familiar with either and or by using yield keywords -

  IRB & gt; DEAF Methectaptures (RGR, and Block) Blockcode (AGR, 0) + BlockCol (Arg., Reverse, 1) and # = & gt; Neil Ibarb & gt; Meth_captures ('pony') do. Word, number "Callback in! Word = # {word.inspect}, num = # {num.inspect}" ends in word + num.to_s callback! In the callback, the word = "pony" number = 0! Word = "yunp" number = 1 # = & gt; "Pani 0 Jonop 1" IRB & gt; Def Meth_ields (RGR) yield (AGR, 0) + yield (RG upscale, 1) and # = & gt; Neil Ibarb & gt; Meth_ild ('frog'). Word, number "Callback in! Word = # {word.inspect}, num = # {num.inspect}" ends in word + num.to_s callback! Word = "frog", call = num = 0 in the callback! Word = "FROG", num = 1 # = & gt; "Frog0FROG1"  

Note that our callback was the same in every case - we can remove the recurrence by saving our callback in an object, and then can pass it in each method. It can be done by using lambda to capture callback in an object, and then it can be done with & amp; By prefixing it with can be passed a method.

  IRB & gt; Callback = Lambda | Word, number Say "Callback in! Word = # {word.inspect}, num = # {num.inspect}", the word + num.to_s end # => # & Lt; Proc: 0x0052e3d8 @ (IRB): 22 & gt; IRB & gt; Methampamps ('unicorn', and callback) in callback! Word = "unicorn", call = num = 0 in callback! Word = "nrocinu", num = 1 # = & gt; "Unicorn 0 NCCN1" IRB & gt; Math_Ideal ('Plate', and Callback) in Callback! Word = "plate", callback = num = 0! Word = "plate", number = 1 # = & gt; It is important to understand the various uses of the  

and for the final argument of the function as a prefix

• A function definition
• In a function call, it spreads a callback object to a block

If you see all the The blocks around the place are used, especially in the operators, like Array # every .