Inference failure with for-loop and associated type that contains lifetimes #22066
Labels
A-associated-items
Area: Associated items (types, constants & functions)
E-needs-test
Call for participation: An issue has been fixed and does not reproduce, but no test has been added.
Comments
steveklabnik
added
I-ICE
|
The ICE is due to #20300, which already has an fix about to be merged. With that out of the way, the more interesting issue here is the type inference error. The compiler is happy if #[cfg(not(works))]
pub trait LineFormatter<'a> {
type Iter: Iterator<Item=&'a str> + 'a;
fn iter(&'a self, line: &'a str) -> Self::Iter;
fn dimensions(&'a self, line: &'a str) {
for _grapheme in self.iter(line) {
}
}
}
#[cfg(works)]
pub trait LineFormatter {
type Iter: Iterator<Item=&'static str>;
fn iter<'a>(&'a self, line: &'a str) -> Self::Iter;
fn dimensions<'a>(&'a self, line: &'a str) {
for _grapheme in self.iter(line) {
}
}
}
fn main() {}It is probably related to #21974. And this ticket could use a more precise title; it is more about trait lifetime parameter interferes with type inference than ICE. |
edwardw
added a commit
to edwardw/rust
that referenced
this issue
Feb 22, 2015
|
as @edwardw says, the ICE here is fixed. @steveklabnik could you remove the label? |
steveklabnik
removed
the
I-ICE
arielb1
changed the title
|
The inference problem also occurs with pub trait LineFormatter<'a> {
type Iter: Iterator<Item=&'a str> + 'a;
fn iter(&'a self, line: &'a str) -> Self::Iter;
fn dimensions(&'a self, line: &'a str) {
let mut iter: Self::Iter = self.iter(line);
<_ as IntoIterator>::into_iter(iter);
}
}
fn main() {} |
|
I think I still got this ICE. The error: Extracting the code as best I can I got it down to the following: use std::marker::PhantomData;
pub struct GILGuard;
trait PythonObject<'a> {
fn dummy() -> &'a i32;
}
#[derive(Copy, Clone)]
pub struct Python<'p>(PhantomData<&'p GILGuard>);
pub struct PyErr<'p> {
pub ptype : PyObject<'p>,
}
type PyResult<'p, T> = Result<T, PyErr<'p>>;
pub struct PyObject<'a> {
dummy : &'a i32
}
impl <'p> PyObject<'p> {
pub fn cast_into<T>(self) -> Result<T, PythonObjectDowncastError<'p>> where T: PythonObjectWithCheckedDowncast<'p> {
PythonObjectWithCheckedDowncast::downcast_from(self)
}
}
pub struct PythonObjectDowncastError<'p>(pub Python<'p>);
pub trait PythonObjectWithCheckedDowncast<'p> : PythonObject<'p> {
fn downcast_from(PyObject<'p>) -> Result<Self, PythonObjectDowncastError<'p>>;
}
impl <'p> PythonObjectWithCheckedDowncast<'p> for PyObject<'p> {
#[inline]
fn downcast_from(obj: PyObject<'p>) -> Result<PyObject<'p>, PythonObjectDowncastError<'p>> {
Ok(obj)
}
}
impl <'p> PythonObject<'p> for PyObject<'p> {
fn dummy() -> &'p i32 { &7 }
}
pub trait PyExtractor<'python, 'source, 'prepared> {
type Prepared;
fn extract<T>(prepared: &'prepared Self::Prepared) -> PyResult<'python, T>
where T: PythonObjectWithCheckedDowncast<'python> ;
}
pub struct PyObjectExtractor;
impl <'python, 'source, 'prepared> PyExtractor<'python, 'source, 'prepared>
for PyObjectExtractor {
type Prepared = &'source PyObject<'python>;
#[inline]
fn extract<T>(&&ref obj: &'prepared Self::Prepared) -> PyResult<'python, T>
where T: PythonObjectWithCheckedDowncast<'python> {
Ok(try!(obj.clone().cast_into()))
}
}
pub trait ExtractPyObject<'python, 'source, 'prepared> {
type Prepared;
fn prepare_extract(obj: &'source PyObject<'python>) -> PyResult<'python, Self::Prepared>;
fn extract<E: PyExtractor<'python, 'source, 'prepared>>(prepared: &'prepared Self::Prepared) -> PyResult<'python, Self>;
}
impl <'python, 'source, 'prepared, T> ExtractPyObject<'python, 'source, 'prepared>
for T where T: PythonObjectWithCheckedDowncast<'python> {
type Prepared = &'source PyObject<'python>;
#[inline]
fn prepare_extract(obj: &'source PyObject<'python>) -> PyResult<'python, Self::Prepared> {
Ok(obj)
}
#[inline]
fn extract<E: PyExtractor<'python, 'source, 'prepared>>(&&ref obj: &'prepared Self::Prepared) -> PyResult<'python, T> {
E::extract::<Self::Prepared>(&obj)
}
} |
arielb1
added
the
E-needs-test
|
This seems to work on Rust 1.10. |
bors
added a commit
that referenced
this issue
May 3, 2017
…alexcrichton Add test for an inference failure. Fixes #22066
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System Info:
I'm trying to create a trait for formatting lines of text (e.g. do line wrapping, manage font size, etc.). I want implementers to only have to provide an iterator and a method for producing those iterators, and everything else is provided with default implementations that utilize those.
The following is a minified version of what I'm trying to do that produced an error.
Code:
Error:
This error seems strange enough on its own, because rustc ought to be able to infer the type of
graphemefrom the return type ofSelf::Iter::next(). So I thought perhaps the problem is that it somehow lacked type information aboutself.iter(). Thus I changed the code so that the iterator type is explicit, and got a different error:Code:
Error (with backtrace):
I wouldn't be surprised if I'm implementing this stuff wrong, but since it's producing an ICE it seemed like I ought to submit a bug report.
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