Implement data directory for #8

[jfinkhaeuser]

Fixes #8 when merged.

Following the whitepaper is a little more complex than the issue bullet list describes.

Missing:

• tests
• a README, describing the flows (from the whitepaper)

[jfinkhaeuser]

I'm running into some issues with the tests. Basically, I can't find a way to create account IDs in my mocks. There doesn't seem to be any sort of constructor for T::AccountId that I can find. When I try to initialize it from an u64 (because in the mocks, that's what it is), there's an error that an associated type was expected. When I try to initialize it from an empty struct {}, I get errors that the type is u64, so I can't use that constructor.

It's really frustrating to say the least.

It seems as if rust is smart enough to be type safe with its abstract types, but then only selectively smart enough to know what concrete type it's dealing with.

[jfinkhaeuser]

@mnaamani @siman I realize that tests are still missing, but if you have feedback already, that'd be great!

[mnaamani]

@jfinkhaeuser

This doesn't work?

const Alice: u64 = 1;

or

let Alice = 1 as u64;

Overkill but this could work also:

let Alice = <Test as system::Trait>::AccountId::sa(1);

[jfinkhaeuser]

Looks in the mocks, it complains that there's an issue with the As trait not being implemented or something. I can paste the error. It's a bit of a mystery to me, as the things that work elsewhere don't seem to work in the mock.

[jfinkhaeuser]

Casting via as keyword doesn't work; there's an error saying that you can only use it on primitive types. You and I know that AccountId is a u64, but apparently the rust compiler doesn't within this context.

[mnaamani]

Yes you will need to have the As trait in scope.

use runtime_primitives::traits::As

[jfinkhaeuser]

error[E0599]: no function or associated item named `sa` found for type `<T as srml_system::Trait>::AccountId` in the current scope
  --> src/storage/mock.rs:66:35
   |
66 |             origin: T::AccountId::sa(1),
   |                     --------------^^
   |                     |
   |                     function or associated item not found in `<T as srml_system::Trait>::AccountId`

and

error[E0308]: mismatched types
  --> src/storage/mock.rs:66:21
   |
66 |             origin: 1 as u64,
   |                     ^^^^^^^^ expected associated type, found u64
   |
   = note: expected type `<T as srml_system::Trait>::AccountId`
              found type `u64`

respectively.

The As trait should be in scope; if I use it explicitly, there's another error again.

[jfinkhaeuser]

As best as I can read it, the issue is that system::Trait doesn't actually define what AccountId is, so the compiler can't infer that as should exist. Because what we really are using is the Test struct for which the trait is implemented.

I also experimented with Test::AccountId to no avail.

[mnaamani]

let Alice = <Test as system::Trait>::AccountId::sa(1);

Test not T

[jfinkhaeuser]

Same difference, the first of the two errors above happen.

[jfinkhaeuser]

I just had another idea, though...

[jfinkhaeuser]

Nope, same issue.

[jfinkhaeuser]

I think this is done, actually. Let me know if there's still something pressing.