Change From<&'a [u8]> to an explicit function

[seanmonstar]

Most of the From conversions to Bytes are shallow copies, just grabbing a pointer and pulling it in. There is also the from_static function to save copying a static set of bytes. However, the From<&'a [u8]> impl will copy the slice into a new buffer (either inline or a new heap allocation, depending on size).

Unfortunately, that &'a [u8] means it applies to &'static [u8] as well. In cases where one is generic over Into<Bytes>, a user can easily and accidentally cause copies of static slices, instead of remembering to call Bytes::from_static. This issue proposes to change the defaults, so that the faster way is easier.

• Remove From<&'a [u8]> for Bytes/BytesMut.
• Add From<&'static [u8]> for Bytes/BytesMut.
• Add a new constructor that can take &'a [u8], that explicitly shows a copy will happen.

The name of this new method could be a few things, these just some examples that occurred to me:

• Bytes::copy(slice)
• Bytes::copy_from(slice)

[seanmonstar]

Oh, this would be a breaking change, so would require (block?) 0.5.

[YetAnotherMinion]

Just to clarify,

From<&'a [u8]> for BytesMut can stay because static slices are not mutable, so a copy has to happen from the 'static slice when creating BytesMut.

So only Bytes would have its From<&'a [u8]> removed.

[carllerche]

Mentioned by @arthurprs:

While I understand the reasoning this severely limits Byte as a Vec replacement, like backing a https://crates.io/crates/string

Specifically, this issue: carllerche/string#6