tests/ui-fulldeps/issue-11881.rs

   1 // run-pass
   2
   3 #![allow(unused_must_use)]
   4 #![allow(dead_code)]
   5 #![allow(unused_imports)]
   6
   7 use std::fmt;
   8 use std::io::prelude::*;
   9 use std::io::Cursor;
  10 use std::slice;
  11 use std::marker::PhantomData;
  12
  13 trait Encoder {
  14     type Error;
  15 }
  16
  17 trait Encodable<S: Encoder> {
  18     fn encode(&self, s: &mut S) -> Result<(), S::Error>;
  19 }
  20
  21 struct JsonEncoder<'a>(PhantomData<&'a mut ()>);
  22
  23 impl Encoder for JsonEncoder<'_> {
  24     type Error = ();
  25 }
  26
  27 struct AsJson<'a, T> {
  28     inner: &'a T,
  29 }
  30
  31 impl<'a, T: for<'r> Encodable<JsonEncoder<'r>>> fmt::Display for AsJson<'a, T> {
  32     /// Encodes a json value into a string
  33     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> fmt::Result {
  34         Ok(())
  35     }
  36 }
  37
  38 fn as_json<T>(t: &T) -> AsJson<'_, T> {
  39     AsJson { inner: t }
  40 }
  41
  42 struct OpaqueEncoder(Vec<u8>);
  43
  44 impl Encoder for OpaqueEncoder {
  45     type Error = ();
  46 }
  47
  48
  49 struct Foo {
  50     baz: bool,
  51 }
  52
  53 impl<S: Encoder> Encodable<S> for Foo {
  54     fn encode(&self, _s: &mut S) -> Result<(), S::Error> {
  55         Ok(())
  56     }
  57 }
  58
  59 struct Bar {
  60     froboz: usize,
  61 }
  62
  63 impl<S: Encoder> Encodable<S> for Bar {
  64     fn encode(&self, _s: &mut S) -> Result<(), S::Error> {
  65         Ok(())
  66     }
  67 }
  68
  69 enum WireProtocol {
  70     JSON,
  71     Opaque,
  72     // ...
  73 }
  74
  75 fn encode_json<T: for<'a> Encodable<JsonEncoder<'a>>>(val: &T, wr: &mut Cursor<Vec<u8>>) {
  76     write!(wr, "{}", as_json(val));
  77 }
  78
  79 fn encode_opaque<T: Encodable<OpaqueEncoder>>(val: &T, wr: Vec<u8>) {
  80     let mut encoder = OpaqueEncoder(wr);
  81     val.encode(&mut encoder);
  82 }
  83
  84 pub fn main() {
  85     let target = Foo { baz: false };
  86     let proto = WireProtocol::JSON;
  87     match proto {
  88         WireProtocol::JSON => encode_json(&target, &mut Cursor::new(Vec::new())),
  89         WireProtocol::Opaque => encode_opaque(&target, Vec::new()),
  90     }
  91 }