Loading up a hash with variables if they are defined

ruby-talk
1

Is there a cleaner, more Rubyesque way to do this?

  # Return a hash of the navigation parameters
  def nav_params
    params = {}

    params[:prefix] = @prefix if @prefix
    params[:category_id] = @category_id if @category_id
    params[:page] = @page if @page

    params
  end

I want to load a parameters hash with the contents of some instance
variables, but only if they are defined.

--wpd

2

# Return a hash of the navigation parameters
def nav_params
   params = {}

   params[:prefix] = @prefix if @prefix
   params[:category_id] = @category_id if @category_id
   params[:page] = @page if @page

   params
end

I want to load a parameters hash with the contents of some instance
variables, but only if they are defined.

params = [:prefix, :category_id, :page].inject({}) do |hash, name|
  var = instance_variable_get("@#{name}")
  hash[name] = var if var
  hash
end

3

irb(main):005:0> {:prefix => @prefix, :category_id => @category, :page
=> @page}.reject {|k,v| v.nil?}
=> {:prefix=>"asdasdf", :category_id=>"cat"}

Jesus.

···

On Tue, Dec 23, 2008 at 5:51 PM, Patrick Doyle <wpdster@gmail.com> wrote:

Is there a cleaner, more Rubyesque way to do this?

# Return a hash of the navigation parameters
def nav_params
   params = {}

   params[:prefix] = @prefix if @prefix
   params[:category_id] = @category_id if @category_id
   params[:page] = @page if @page

   params
end

I want to load a parameters hash with the contents of some instance
variables, but only if they are defined.

4

Patrick Doyle wrote:

Is there a cleaner, more Rubyesque way to do this?

  # Return a hash of the navigation parameters
  def nav_params
    params = {}

    params[:prefix] = @prefix if @prefix
    params[:category_id] = @category_id if @category_id
    params[:page] = @page if @page

    params
  end

I want to load a parameters hash with the contents of some instance
variables, but only if they are defined.

Watch out: "only if they are defined" is not the same as "only if they are not nil or false". If you want the former, then this might be what you are looking for:

class C
   NAV_VARS = %w{ @prefix @category_id @page }
   NAV_VAR_KEYS = NAV_VARS.inject({}) {|h,v| h[v] = v.delete("@").to_sym; h}

   def nav_params
     (instance_variables & NAV_VARS).inject({}) do |params,var|
       params[NAV_VAR_KEYS[var]] = instance_variable_get(var)
       params
     end
   end
end

c = C.new
c.instance_eval do
   @prefix = "foo"
   @page = false
end

p c.nav_params # ==> {:prefix=>"foo", :page=>false}

···

--
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

5

Thanks... that's certainly along the lines of what I was searching for.
I'll go read about #instance_variable_get now.

--wpd

···

On Tue, Dec 23, 2008 at 11:57 AM, James Coglan <jcoglan@googlemail.com>wrote:

>
> # Return a hash of the navigation parameters
> def nav_params
> params = {}
>
> params[:prefix] = @prefix if @prefix
> params[:category_id] = @category_id if @category_id
> params[:page] = @page if @page
>
> params
> end
>
> I want to load a parameters hash with the contents of some instance
> variables, but only if they are defined.

params = [:prefix, :category_id, :page].inject({}) do |hash, name|
var = instance_variable_get("@#{name}")
hash[name] = var if var
hash
end