mirror of https://github.com/rust-lang/rust
92 lines
1.7 KiB
Rust
92 lines
1.7 KiB
Rust
//@ run-pass
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#![allow(unused_must_use)]
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#![allow(dead_code)]
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#![allow(unused_imports)]
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use std::fmt;
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use std::io::prelude::*;
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use std::io::Cursor;
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use std::slice;
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use std::marker::PhantomData;
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trait Encoder {
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type Error;
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}
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trait Encodable<S: Encoder> {
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fn encode(&self, s: &mut S) -> Result<(), S::Error>;
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}
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struct JsonEncoder<'a>(PhantomData<&'a mut ()>);
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impl Encoder for JsonEncoder<'_> {
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type Error = ();
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}
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struct AsJson<'a, T> {
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inner: &'a T,
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}
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impl<'a, T: for<'r> Encodable<JsonEncoder<'r>>> fmt::Display for AsJson<'a, T> {
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/// Encodes a json value into a string
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fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> fmt::Result {
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Ok(())
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}
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}
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fn as_json<T>(t: &T) -> AsJson<'_, T> {
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AsJson { inner: t }
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}
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struct OpaqueEncoder(Vec<u8>);
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impl Encoder for OpaqueEncoder {
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type Error = ();
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}
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struct Foo {
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baz: bool,
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}
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impl<S: Encoder> Encodable<S> for Foo {
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fn encode(&self, _s: &mut S) -> Result<(), S::Error> {
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Ok(())
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}
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}
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struct Bar {
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froboz: usize,
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}
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impl<S: Encoder> Encodable<S> for Bar {
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fn encode(&self, _s: &mut S) -> Result<(), S::Error> {
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Ok(())
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}
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}
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enum WireProtocol {
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JSON,
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Opaque,
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// ...
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}
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fn encode_json<T: for<'a> Encodable<JsonEncoder<'a>>>(val: &T, wr: &mut Cursor<Vec<u8>>) {
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write!(wr, "{}", as_json(val));
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}
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fn encode_opaque<T: Encodable<OpaqueEncoder>>(val: &T, wr: Vec<u8>) {
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let mut encoder = OpaqueEncoder(wr);
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val.encode(&mut encoder);
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}
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pub fn main() {
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let target = Foo { baz: false };
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let proto = WireProtocol::JSON;
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match proto {
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WireProtocol::JSON => encode_json(&target, &mut Cursor::new(Vec::new())),
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WireProtocol::Opaque => encode_opaque(&target, Vec::new()),
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}
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}
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