Calling Rust from Crystal

README.md

Demonstrates how to link Rust code in Crystal (on MacOS).

See the Makefile; the Rust crate is built as a dylib, and the Crystal code then uses the linked library. Fairly simple.

Following both Rust and Crystal conventions, lib.rs and foo.cr need to be in a src/ directory; everything else is in the root.

Calling Rust from Crystal

# Makefile
lib = target/debug/foo.dylib
app = bin/foo

all: $(app)

$(lib): src/lib.rs Cargo.toml
	cargo build

$(app): $(lib) src/foo.cr
	LIBRARY_PATH=$(PWD)/target/debug:$(LIBRARY_PATH) shards build

clean:
	rm -r $(app) $(dylib)

Cargo.toml

[package]
name = "foo"
version = "0.1.0"
edition = "2021"

[lib]
name = "foo"
crate-type = ["dylib"]

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]

foo.cr

@[Link("foo")]
lib R
  fun foo() : UInt8*
  fun bar() : UInt8*
end

module Foo
  def self.foo
    String.new(R.foo())
  end

  def self.bar
    String.new(R.bar())
  end
end

puts Foo.foo()
puts Foo.bar()

lib.rs

#[no_mangle]
pub extern "C" fn foo() -> *const u8 {
  "Foo from Rust\0".as_bytes().as_ptr()
} 

#[no_mangle]
pub extern "C" fn bar() -> *const u8 {
  "Bar from Rust\0".as_bytes().as_ptr()
}

shard.yml

name: foo
version: 0.1.0

authors:
  - bjjb <jj@bjjb.org>

targets:
  foo:
    main: src/foo.cr

crystal: 1.3.2

license: MIT