Sinatra Locals vs. Instance Variables

Question

What exactly are Sinatra’s locals, and is there any difference between using them in templates as opposed to instance variables? Here’s what I mean by locals:

erb :template, :locals => {:variable => 'value'}

Edit:

In terms of implementation, what are the differences between instance and local variables, and are there any benefits to using one over the other?

Answer 1

From Sinatra's intro:

Templates are evaluated within the same context as route handlers. Instance variables set in route handlers are directly accessible by templates:

get '/:id' do
  @foo = Foo.find(params[:id])
  haml '%h1= @foo.name'
end

Or, specify an explicit Hash of local variables:

get '/:id' do
  foo = Foo.find(params[:id])
  haml '%h1= bar.name', :locals => { :bar => foo }
end

This is typically used when rendering templates as partials from within other templates.

And for some templates there is (for Radius in this case):

Since you cannot call Ruby methods directly from a Radius template, you almost always want to pass locals to it.