1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
// SPDX-License-Identifier: Apache-2.0 OR MIT

/*!
<!-- tidy:crate-doc:start -->
\#\[derive(Read, Write, Seek, BufRead)\] for enums.

## Usage

Add this to your `Cargo.toml`:

```toml
[dependencies]
io-enum = "1"
```

*Compiler support: requires rustc 1.56+*

## Examples

```rust
use std::{
    fs::File,
    io::{self, Write},
    path::Path,
};

use io_enum::*;

#[derive(Read, Write, Seek, BufRead)]
enum Either<A, B> {
    A(A),
    B(B),
}

fn func(path: Option<&Path>) -> impl Write {
    if let Some(path) = path {
        Either::A(File::open(path).unwrap())
    } else {
        Either::B(io::stdout())
    }
}
```

See [auto_enums] crate for how to automate patterns like this.

## Supported traits

- [`Read`](https://doc.rust-lang.org/std/io/trait.Read.html) - [example](https://github.com/taiki-e/io-enum/blob/HEAD/tests/expand/read.rs) | [generated code](https://github.com/taiki-e/io-enum/blob/HEAD/tests/expand/read.expanded.rs)
- [`BufRead`](https://doc.rust-lang.org/std/io/trait.BufRead.html) - [example](https://github.com/taiki-e/io-enum/blob/HEAD/tests/expand/buf_read.rs) | [generated code](https://github.com/taiki-e/io-enum/blob/HEAD/tests/expand/buf_read.expanded.rs)
- [`Write`](https://doc.rust-lang.org/std/io/trait.Write.html) - [example](https://github.com/taiki-e/io-enum/blob/HEAD/tests/expand/write.rs) | [generated code](https://github.com/taiki-e/io-enum/blob/HEAD/tests/expand/write.expanded.rs)
- [`Seek`](https://doc.rust-lang.org/std/io/trait.Seek.html) - [example](https://github.com/taiki-e/io-enum/blob/HEAD/tests/expand/seek.rs) | [generated code](https://github.com/taiki-e/io-enum/blob/HEAD/tests/expand/seek.expanded.rs)

## Related Projects

- [auto_enums]: A library for to allow multiple return types by automatically generated enum.
- [derive_utils]: A procedural macro helper for easily writing [derives macros][proc-macro-derive] for enums.
- [iter-enum]: \#\[derive(Iterator, DoubleEndedIterator, ExactSizeIterator, FusedIterator, Extend)\] for enums.

[auto_enums]: https://github.com/taiki-e/auto_enums
[derive_utils]: https://github.com/taiki-e/derive_utils
[iter-enum]: https://github.com/taiki-e/iter-enum
[proc-macro-derive]: https://doc.rust-lang.org/reference/procedural-macros.html#derive-macros

<!-- tidy:crate-doc:end -->
*/

#![doc(test(
    no_crate_inject,
    attr(
        deny(warnings, rust_2018_idioms, single_use_lifetimes),
        allow(dead_code, unused_variables)
    )
))]
#![forbid(unsafe_code)]

use derive_utils::quick_derive;
use proc_macro::TokenStream;

#[proc_macro_derive(Read)]
pub fn derive_read(input: TokenStream) -> TokenStream {
    // TODO: Add is_read_vectored once stabilized https://github.com/rust-lang/rust/issues/69941
    // TODO: Add read_buf,read_buf_exact once stabilized https://github.com/rust-lang/rust/issues/78485
    quick_derive! {
        input,
        ::std::io::Read,
        trait Read {
            #[inline]
            fn read(&mut self, buf: &mut [u8]) -> ::std::io::Result<usize>;
            #[inline]
            fn read_vectored(
                &mut self, bufs: &mut [::std::io::IoSliceMut<'_>],
            ) -> ::std::io::Result<usize>;
            #[inline]
            fn read_to_end(&mut self, buf: &mut ::std::vec::Vec<u8>) -> ::std::io::Result<usize>;
            #[inline]
            fn read_to_string(
                &mut self,
                buf: &mut ::std::string::String,
            ) -> ::std::io::Result<usize>;
            #[inline]
            fn read_exact(&mut self, buf: &mut [u8]) -> ::std::io::Result<()>;
        }
    }
}

#[proc_macro_derive(Write)]
pub fn derive_write(input: TokenStream) -> TokenStream {
    // TODO: Add is_write_vectored once stabilized https://github.com/rust-lang/rust/issues/69941
    // TODO: Add write_all_vectored once stabilized https://github.com/rust-lang/rust/issues/70436
    quick_derive! {
        input,
        ::std::io::Write,
        trait Write {
            #[inline]
            fn write(&mut self, buf: &[u8]) -> ::std::io::Result<usize>;
            #[inline]
            fn write_vectored(
                &mut self,
                bufs: &[::std::io::IoSlice<'_>],
            ) -> ::std::io::Result<usize>;
            #[inline]
            fn flush(&mut self) -> ::std::io::Result<()>;
            #[inline]
            fn write_all(&mut self, buf: &[u8]) -> ::std::io::Result<()>;
            #[inline]
            fn write_fmt(&mut self, fmt: ::std::fmt::Arguments<'_>) -> ::std::io::Result<()>;
        }
    }
}

#[proc_macro_derive(Seek)]
pub fn derive_seek(input: TokenStream) -> TokenStream {
    quick_derive! {
        input,
        ::std::io::Seek,
        trait Seek {
            #[inline]
            fn seek(&mut self, pos: ::std::io::SeekFrom) -> ::std::io::Result<u64>;
        }
    }
}

#[proc_macro_derive(BufRead)]
pub fn derive_buf_read(input: TokenStream) -> TokenStream {
    quick_derive! {
        input,
        ::std::io::BufRead,
        trait BufRead {
            #[inline]
            fn fill_buf(&mut self) -> ::std::io::Result<&[u8]>;
            #[inline]
            fn consume(&mut self, amt: usize);
            #[inline]
            fn read_until(
                &mut self, byte: u8, buf: &mut ::std::vec::Vec<u8>,
            ) -> ::std::io::Result<usize>;
            #[inline]
            fn read_line(&mut self, buf: &mut ::std::string::String) -> ::std::io::Result<usize>;
        }
    }
}