rails api dock syntax

Question

ROR Api Dock always starts with a syntax of the method. My example will be link_to:

link_to(name = nil, options = nil, html_options = nil, &block) public

My question is on the "name=nil" or "something = nil" which i see on most every command.

A second example: url_for(options = nil)

Can someone explain what is the point of this or what it is trying to say..does it mean that the option is optional?

Why is it important..

It means that it also accepts `nil` for that argument. – Pavan Apr 28 '16 at 13:11 — Pavan, Apr 28 '16 at 13:11

score 1 · Answer 1 · answered Apr 28 '16 at 14:35

Ruby unlike for example JavaScript or PHP enforces the number of arguments a method is called with:

def foo(a,b) 
end

So if you call foo with no arguments Ruby will raise an exception ArgumentError: wrong number of arguments (0 for 2).

By setting a default value, you mark a argument as optional:

def foo(a = nil, b = nil) 
end

Calling foo with no arguments will no longer raise an error.

This is often used to create methods that can take list arguments or a hash:

def foo(a = nil, b = nil, opts = {})
  opts.each do |k,v|
    puts "#{k} : #{v}"
  end
end

As to why Ruby does this - its a language design decision. It does in many cases help track down simple bugs where you are simply passing the wrong arguments. In a language that does not enforce this you would get a type or undefined error from inside the method which is harder to spot the root cause of. IMHO Matz got this one right.

rails api dock syntax

1 Answers1