goish

Write Rust using Go idioms.

goish is a Rust crate that ports Go's standard library and built-in syntax constructs into Rust so that Go programmers can write Rust code that reads and feels like Go — (val, err) := fn(), if err != nil, defer f.Close(), go func() { ... }(), for i, v := range slice, []string{"a","b"} — while still getting Rust's safety and performance under the hood.

use goish::prelude::*;

fn divide(a: int64, b: int64) -> (int64, error) {
    if b == 0 {
        return (0, errors::New("divide by zero"));
    }
    (a / b, nil)
}

fn main() {
    fmt::Println!("hello", "world", 42);

    let (q, err) = divide(10, 0);
    if err != nil {
        fmt::Println!("error:", err);
    } else {
        fmt::Printf!("q = %d\n", q);
    }

    let names = slice!([]string{"alice", "bob", "carol"});
    let env   = map!([string]int{"PORT" => 5432, "TTL" => 60});

    fmt::Printf!("%d names, %d env vars\n", len!(names), len!(env));

    defer!{ fmt::Println!("bye!"); }
}

Install

Add to Cargo.toml:

[dependencies]
goish = { git = "https://github.com/chanwit/goish" }

Or, from crates.io:

[dependencies]
goish = "0.11"     # latest

Then in every file where you want Go-shaped code:

use goish::prelude::*;

Cheat-sheet

Types

Composite literals

Builtins

Errors

let err = errors::New("not found");
let wrapped = errors::Wrap(err.clone(), "lookup failed");
if errors::Is(&wrapped, &err) { ... }

errors::New returns error directly — no Some/Ok wrapping. err != nil works because error implements PartialEq<error> with the nil constant.

fmt and Stringer

fmt::Println!("n =", 42);
let s = fmt::Sprintf!("%-8s = %d", "answer", 42);
let e = fmt::Errorf!("code %d: %s", 500, "oops");

struct Color { r: int, g: int, b: int }
fmt::stringer! {
    impl Color {
        fn String(&self) -> string {
            fmt::Sprintf!("#%02x%02x%02x", self.r, self.g, self.b)
        }
    }
}
fmt::Println!("color:", Color { r: 255, g: 0, b: 0 }); // → color: #ff0000

Goroutines and channels

let jobs: Chan<int> = chan!(int, 4);
let g = go!{
    for i in 1..=3 {
        jobs.Send(i);           // looks sync, proc-macro rewrites to .send(i).await
    }
};
for _ in 0..3 {
    let (v, _) = jobs.Recv();
    fmt::Printf!("got: %d\n", v);
}
let _ = g.Wait();

Goroutines run as tokio async tasks — ~200 B each. Proven at 1,000,000 concurrent goroutines (see tests/million_goroutines.rs), which is what Go's scheduler handles natively. Inside go!{}, channel method calls look identical to outside — a proc-macro (goish-macros) rewrites .Send, .Recv, .Wait into their async equivalents at compile time.

net/http

use goish::prelude::*;

fn main() {
    http::HandleFunc("/hello", |w, r| {
        Fprintf!(w, "hi %s", r.URL.Path);
    });
    log::Fatalf!("%s", http::ListenAndServe(":8080", nil));
}

Client:

let (mut resp, err) = http::Get("http://api.example.com/v1/status");
if err != nil { log::Fatalf!("%s", err); }
defer!{ resp.Body.Close(); }
let body = resp.Body.String();
fmt::Println!(body);

Context-bound deadlines cancel in-flight requests, same shape as Go:

let (ctx, _) = context::WithTimeout(context::Background(), 5i64 * time::Second);
let (req, _) = http::NewRequestWithContext(ctx, "GET", url, &[]);
let (resp, err) = http::Do(req);   // aborts after 5s if server is slow

Inside handlers, select! on r.Context().Done() to abort work when the client disconnects. Backed by hyper 1.x + tokio; goroutine-per-connection.

defer!

fn foo() {
    defer!{ fmt::Println!("cleanup"); }
    defer!{ fmt::Println!("inner"); }
    fmt::Println!("work");
}
// prints: work, inner, cleanup   (LIFO, same as Go)

sync

let mu = sync::Mutex::new(0i64);
{ let mut g = mu.Lock(); *g += 1; }    // auto-unlock at scope end

let wg = sync::WaitGroup::new();
for _ in 0..4 {
    wg.Add(1);
    let w = wg.clone();
    go!{ do_work(); w.Done(); };
}
wg.Wait();

time

let start = time::Now();
time::Sleep(time::Millisecond * 100i64);
let elapsed = time::Since(start);
fmt::Printf!("took %s\n", elapsed);   // e.g. "100.3ms"

testing (v0.4) — port Go tests line-by-line

use goish::prelude::*;

// Go:   type PathTest struct { path, result string }
Struct!{ type PathTest struct { path, result string } }

// Go:   var tests = []PathTest{ {"", "."}, {"abc", "abc"}, ... }
fn tests() -> slice<PathTest> { slice!([]PathTest{
    PathTest!("",    "."),
    PathTest!("abc", "abc"),
    // ...
})}

test!{ fn TestClean(t) {
    for test in &tests() {
        let s = path::Clean(&test.path);
        if s != test.result {
            t.Errorf(Sprintf!("Clean(%q) = %q, want %q", test.path, s, test.result));
        }
    }
}}

benchmark!{ fn BenchmarkJoin(b) {
    b.ReportAllocs();
    while b.Loop() {
        path::Join(&slice!([]string{"a", "b"}));
    }
}}

Go's TestMain ports as test_main! with a custom harness. In a harness = false test target, use test_h! (not test!) and wire setup/teardown around m.Run():

// tests/my_test.rs — registered with harness = false in Cargo.toml
use goish::prelude::*;

test_h!{ fn TestAddition(t) { if 2+2 != 4 { t.Error("math broke"); } } }

test_main!{ fn TestMain(m) {
    setup();
    let code = m.Run();
    teardown();
    os::Exit(code);
}}

Real Go tests ported as regression fixtures live in tests/:

• tests/path_test.rs — direct port of go/src/path/path_test.go
• tests/itoa_test.rs — direct port of go/src/strconv/itoa_test.go
• tests/strings_compare_test.rs — port of go/src/strings/compare_test.go
• tests/bytes_test.rs — subset of go/src/bytes/bytes_test.go (Equal/Index/LastIndex/IndexByte)

Go's defer-recover ports as recover!{ … }:

// Go:   defer func() { if r := recover(); r == nil { t.Fatal("want panic") } }()
//       doPanickyThing()
let r = recover!{ strconv::FormatUint(12345678, 1) };
if r.is_none() { t.Fatal("expected panic"); }

Packages (current status)

Known gaps

• string is an alias for String (owned, mutable). Go strings are immutable shared bytes; close enough for most code.

Examples

cargo run --example hello       # (val, err), Stringer, bytes.Buffer
cargo run --example config      # strings + strconv config parser
cargo run --example literals    # slice! / map! / chan! / len / append / delete
cargo run --example worker      # goroutines + channel + defer + time::Since
cargo run --example pipeline    # sync.WaitGroup + sort + math + filepath + log + context
cargo run --example webscrape   # url + regexp + json + csv + sha256 + path  (v0.3)
cargo run --example webserver   # net/http server + client, in Go-shaped Rust (v0.5)

Design priority

The top priority is Go idioms and call-site syntax — if a Go programmer reads a goish program, it should look like Go. Rust idioms (Option, Some, &mut, trait-bound generics) live under the hood. When a Rust idiom has to leak, it's called out explicitly and a wrapper is designed to minimise it.

For the goroutine + channel runtime decision (tokio + flume, 1M goroutines), see docs/scheduler.md.

License

Dual-licensed under either of:

• MIT License
• Apache License, Version 2.0

at your option.