std::slice::from_raw_buf is very unergonomic #20748
Description
The signature of from_raw_buf is:
fn from_raw_buf<T>(p: &'a *const T, len: uint) -> &'a [T]The fact that the lifetime of the returned slice is the same as the lifetime of the pointer is a very bad idea. And now that CVec is gone, this is the only way to build a slice from a raw pointer.
I can see many potential problems, but the ones that I've encountered while removing CVec is that you can't cast your pointers, not even from mut to const: (http://is.gd/eW1KmQ)
struct Foo { data: *mut i8, len: uint }
impl Foo {
fn as_slice(&self) -> &[i8] {
unsafe {
// value "self.data as *const i8" does not live long enough
std::slice::from_raw_buf(&(self.data as *const i8), self.len)
}
}
}And that you can't use raw pointers in iterators anymore: (http://is.gd/UsePsX)
struct Iter<'a> { data: *const u8, marker: ContravariantLifetime<'a> }
impl<'a> Iterator for Iter<'a> {
type Item = &'a [u8];
fn next(&mut self) -> Option<&'a [u8]> {
Some(unsafe {
// cannot infer an appropriate lifetime for borrow expression due to conflicting requirements
std::slice::from_raw_buf(&self.data, 1)
})
}
}If I'm manipulating raw pointers which are unsafe by nature, please let me be unsafe!
The first example can be bypassed by using from_raw_mut_buf and casting the returned &mut [i8] to a &[i8], which means that the unsafe API is more restrictive than the safe API!