Rails validation :if => Proc.new or lambda?

问题:

I have found that in all examples (include rails documentation) that I have seen for the :if option of validation methods uses Proc.new instead of lambda, for example

class Foo < ActiveRecord::Base
  validates_presence_of :name, :if => Proc.new{|f| .... } # why not lambda here?
end

is there any reason for this? As far as I know, lambda

1. Is more strict with arguments.
2. Also return statement in lambda block returns from the block, not from calling function.

Both seems to be desirable behavior for :if option mentioned above, is there anything I am missing?

回答1:

Both seems to be desirable behavior for :if option mentioned above, is there anything I am missing?

I'm guessing that:

It's more desirable to allow Procs as they don't care about the number of arguments. So I could easily write any of the below:

validates_presence_of :name, :if => Proc.new{|f| f.display_name.blank? }    # I care about 'f' here as I need it to check something.

... and:

validates_presence_of :secret_sauce, :if => Proc.new{ MyApp::REQUIRE_SECRET_SAUCE }    # I don't care about any arguments being passed in.

This may seem like a minor thing, but I guess it adds to the flexibility.