Initializing custom variables

[eyalev]

Hi,

Is it possible to initialize custom instance variables in addition to using pattr_initialize ?

For example: @time = Time.now

Thanks

[henrik]

No, sorry. The idea is to remove boilerplate for the most common case, but if you need things like that, or default values etc, just define a regular initializer.

It's mostly that I can't think of a good syntax that isn't too messy or non-obvious. If you can think of something, do suggest it.

[eyalev]

Ok, thanks

[joakimk]

One thing you can do is to use ||= or || to achieve similar effects. It depends on what you need it for.

class Foo
  pattr_initialize :bar

  private

  def time
    @time ||= Time.now
  end

  def bar
    @bar || "default-value"
  end
end

[eyalev]

Good idea, thanks @joakimk

[mcmire]

@henrik Would it be a good idea for attr_initialize and friends to mix in a module so that you can override #initialize and super as needed?

[henrik]

@mcmire Hm, yeah, maybe. I generally like the flexibility you get by adding functionality through mixing in modules.

We do support a block syntax to do things after assigning values, e.g.

pattr_initialize :time do
  @time ||= Time.now
end

Which could help in some cases. But in this example, you would still need to pass a nil value when you initialize: it doesn't make the argument optional.

We've considered supporting optional arguments, but it's hard to think of a syntax for that that isn't super messy. Currently considering if we should just hijack block parameters:

pattr_initialize { |time=Time.now| }