[idea] more compact way to indicate an account stores a particular struct?

[mikemaccana]

So right now we tell Anchor that space is derived from the (currently constant) discriminator size plus INIT_SPACE for the struct:

#[account(
    ...
    space = ANCHOR_DISCRIMINATOR + Offer::INIT_SPACE,
    ...
)]
pub offer: Account<'info, Offer>,

And as you mentioned in #3005 we could have just SPACE (including whatever size the discriminator is):

#[account(
    ...
    space = Offer::SPACE,
    ...
)]
pub offer: Account<'info, Offer>,

Is there any reason we couldn't do something like:

#[account(
    ...
    stores = Offer,
    ...
)]
pub offer: Account<'info, Offer>,

or even:

#[account(
    ...
)]
pub offer: Account<'info, Offer>,

With space being determined by the generic provided to Account<>?

The programmer's intention is to store a struct of a particular type. The fact that the account needs to match the size of the struct is really a dependency of that goal. Also it's easier to reason about!

[acheroncrypto]

Yeah, I've been working on something related that also requires automatic space calculation, so I'm thinking about making the space constraint optional again (it was like that a long time ago).