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Added TryFromCtx impl for &[u8] with no ctx. #102

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Added TryFromCtx impl for &[u8] with no ctx. #102

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Added TryFromCtx impl for &[u8] with no ctx.
Frostie314159 Aug 16, 2024
2d71cd4
rustfmt
Frostie314159 Aug 16, 2024
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38 changes: 23 additions & 15 deletions src/ctx.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -731,6 +731,29 @@ impl<'a> TryIntoCtx for &'a [u8] {
}
}

impl<'a> TryFromCtx<'a, usize> for &'a [u8] {
type Error = error::Error;
#[inline]
fn try_from_ctx(src: &'a [u8], size: usize) -> result::Result<(Self, usize), Self::Error> {
if size > src.len() {
Err(error::Error::TooBig {
size,
len: src.len(),
})
} else {
Ok((&src[..size], size))
}
}
}

impl<'a> TryFromCtx<'a> for &'a [u8] {
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so the problem with having two contexts is that now e.g., this function call becomes ambiguous:

    const buf: &[u8] = &[0x1, 0x2, 0x3, 0x4];
    let res = buf.pread::<&[u8]>(0);

You should see an error like this after a bunch of generic vomit:

error[E0283]: type annotations needed
   --> tests/api.rs:388:19
    |
388 |     let res = buf.pread::<&[u8]>(0);
    |                   ^^^^^
    |
    = note: multiple `impl`s satisfying `&[u8]: TryFromCtx<'_, _>` found in the `scroll` crate:
            - impl<'a> TryFromCtx<'a, usize> for &'a [u8];
            - impl<'a> TryFromCtx<'a> for &'a [u8];

I'm very surprised we do not have a test in either api.rs or somewhere in lib.rs to ensure that existing preads of e.g., &[u8] are compilable. I believe introducing this could theoretically break downstream users as any code that did a pread of &[u8] will no longer compile.

I swear we had tests specifically to test that just pread worked fine on &[u8] but don't see any tests failing...

type Error = error::Error;
#[inline]
fn try_from_ctx(src: &'a [u8], _ctx: ()) -> result::Result<(Self, usize), Self::Error> {
Ok((src, src.len()))
}
}

// TODO: make TryIntoCtx use StrCtx for awesomeness
impl<'a> TryIntoCtx for &'a str {
type Error = error::Error;
Expand Down Expand Up @@ -772,21 +795,6 @@ sizeof_impl!(i128);
sizeof_impl!(f32);
sizeof_impl!(f64);

impl<'a> TryFromCtx<'a, usize> for &'a [u8] {
type Error = error::Error;
#[inline]
fn try_from_ctx(src: &'a [u8], size: usize) -> result::Result<(Self, usize), Self::Error> {
if size > src.len() {
Err(error::Error::TooBig {
size,
len: src.len(),
})
} else {
Ok((&src[..size], size))
}
}
}

impl<'a, Ctx: Copy, T: TryFromCtx<'a, Ctx, Error = error::Error>, const N: usize>
TryFromCtx<'a, Ctx> for [T; N]
{
Expand Down
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