A common requirement with an html first app is to retain the url state as a user clicks around. For example, if a page has a set of scopes and a set of filters, when you’re building the link to a scope, you’ll want to make sure it also includes the currently active filter. 
<a href="<%= current_url_with(scope:'draft') %>">
  Draft 
</a>
<a href="<%= current_url_with(scope:'active') %>">
  Active 
</a>

​
Merge the current url params with a named path

<a href="<%= projects_path(current_params_with(scope:'draft')) %>" >
  Draft Projects 
</a>

​
Likn to a named path with the current url parameters

<a href="<%= projects_path(request.query_parameters) %>" >
  Projects 
</a>

​
Source

These methods are a thin layer on top of Rails’ own methods - url_for and request.query_parameters. 
# /app/helpers/application_helper
def current_url_with(params)
  url_for(request.query_parameters.merge(params))
end

def current_params_with(params)
  request.query_parameters.merge(params)
end