blocks and late evaluation

[Vassilis Vatikiotis]

hi all,

my question is in the context of sinatra but it's a blocks question really.

I have configure block in sinatra (configure blocks in sinatra run only once, upon initialisation). There, I want to load some database records in memory. So I do:
configure do
set :keys do
DB.all.map { |record| record.field }
end
end

Whenever I access the class level variable :keys I get a DB query. Whereas if, inside that configure block, I do:

keys = DB.all.map { |record| record.field }
set :keys, keys

there are no DB queries, I can even stop the database daemon and my app will go on.

Now I'm *almost* certain that it's not a sinatra issue but my ruby block ignorance. I know that Proc objects are evaluated when they are called but here we have a block returning a new Array, and not a Proc object.

can you explain it?
thx

 

[Robert Klemme]

hi all,

my question is in the context of sinatra but it's a blocks question really.

I have configure block in sinatra (configure blocks in sinatra run
only once, upon initialisation). There, I want to load some database
records in memory. So I do:
configure do
set :keys do
DB.all.map { |record| record.field }
end
end

Whenever I access the class level variable :keys I get a DB query.
Whereas if, inside that configure block, I do:

keys = DB.all.map { |record| record.field }
set :keys, keys

there are no DB queries, I can even stop the database daemon and my app will go on.

Now I'm *almost* certain that it's not a sinatra issue but my ruby
block ignorance. I know that Proc objects are evaluated when they are
called but here we have a block returning a new Array, and not a Proc
object.

can you explain it?
thx

I don't know Sinatra (apart from Frank, of course) but the reason must
either be in DB.all's or in set's behavior. To debug it might be
helpful to insert something like "$stderr.puts 'called'" inside the
block so you can see how often the block is invoked.

Kind regards

robert

 

[Fritz Wuehler]

I don't know Sinatra (apart from Frank, of course) but the reason must
either be in DB.all's or in set's behavior. To debug it might be
helpful to insert something like "$stderr.puts 'called'" inside the
block so you can see how often the block is invoked.

That's correct. For Sinatra he should have used DB.all.or.nothing.at.all.

and $when.its.love(there) /= in.between()

I'm surprised somebody else didn't catch this ;-)

 

[Vassilis Vatikiotis]

It's sinatra related after all. set stores the block object and every time :keys is referenced it calls the block.
sorry for of topic and thx