default value in methods

[HenriIV]

hi,

I have problems with default values. I don't know whether I'm stupid or doc is not good (you're not supposed to answer ) but I spend a lot of time for trivial things.

According to Wiki RailsBestPractices, it's a good idea to add a default value like that:

def self.custom_find( id_to_find = 1 )
    ...
end 

When I try to add a default value, I get an error:
[edit: the query is ok without = 0 default value ]

def self.find_query(category, type, city_id, price_min = 0, price_max)
    find(:all,
    sql conditions coming here...)
  end 

parse error, unexpected ')', expecting '='

Did I miss something?

[Fenrir2]

Only the last parameters can have default values. How would you call it otherwise?

find_querycat, :type, :city_id, ????, 100)

??

So ruby is expecting the last parameter to have a default value too. That's why it needs a =, instead of ):

def self.find_query(category, type, city_id, price_min = 0, price_max = 100000) 
                                                                      ^ =, not )

[HenriIV]

thanks Fenrir2, it works but I find it weird as it's not mandatory, just a best practice.
Plus it's not used when the value is empty, it seems to work only with null values.

[Fenrir2]

It's there so you can omit these arguments if you call your procedure. It is by no means a best practice, there are special cases where it is handy. Only use default values if it makes sense.

It is there so you can call your procedure this way:

Foo.find_query(a_category, a_type, a_city_id)

And don't worry about the min/max price.

You cannot do this for a parameter in the middle because it makes no sense to omit it if you have parameters after it.

Another use case is Rails' find. You can use:

Foo.find(23) => find row with id=23

And:

Foo.find(:first, :conditions => 'a = "b"')

So you can use the same method in multiple ways.

[HenriIV]

thanks for the tips Fenrir2