const constructors for hashes about rust-bitcoin

[apoelstra]

PhantomData has only one value, called PhantomData. Use that.

[Kixunil]

FYI I had a PR to do this but it got stale and I'm actually currently working on a replacement since the hash stuff got complicated.

[apoelstra]

from_byte_array and all_zeros could be made const and we could do a point release (assuming there are no other breaking changes in the hashes pipeline yet, which I believe is true).

Actually hashing in constant time is far from trivial, though I haven't tried in a little while.

[Kixunil]

Actually hashing in constant time is far from trivial, though I haven't tried in a little while.

We already have that :)

[apoelstra]

Oh, lol :). So @stevenroose there is a const constructor.

But agreed that all_zeros and from_byte_array should also be const.

[Kixunil]

Definitely!

[tcharding]

Seems that Rust does not allow functions within traits to be marked as const.

ref: https://users.rust-lang.org/t/whats-the-reason-that-fn-in-a-trait-cannot-marked-as-a-const/68636

[apoelstra]

Ah, yeah, that is probably why these aren't const already. We should move those methods out of the trait into inherents.

[Kixunil]

We should move those methods out of the trait into inherents.

Yes!

[15IITian]

rust-bitcoin/hashes/src/sha256t.rs

Line 23 in 9df5963

pub struct Hash<T: Tag>([u8; 32], PhantomData<T>);

In all_zeros and from_byte_array methods in Hash<T> impl -> what should be the value of PhantomData part in it?

[15IITian]

Did anyone also getting same errors while making commits ?