add void repo files

void/notes/multi-language-library.md

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+---
+tags: dev
+---
+
+# Multi Language Library
+
+To create a library that can be used in multiple languages, the language that
+is going to implement the library needs to support [[notes/ffi|FFI]] with the language
+that the library is written in.
+
+With this in, we can use the following in our favor:
+
+- It's impossible that every language support every other language.
+- For compatibility reasons, Almost every language supports C's [[notes/abi|ABI]] for their [[notes/ffi|FFI]].
+- Some compiled language has the avility to compile a C's _"dynamic library"_ (`.so` file in unix and `.dll` in windows).
+- The [[notes/ffi|FFI]] use a _"dynamic library"_ to work.
+
+So, in conclusion: **we can use whatever language that supports compiling to C's ABI to build multi language libraries**
+
+## List of language that compiles to C's ABI
+
+### [[Go]]
+
+To produce a shared library, you need to compile it with compile with: `go build -buildmode=c-shared`.
+
+Note that the documentation says you need to specify with functions needs to be exported:
+
+> Build the listed main package, plus all packages it imports, into a C shared
+> library. The only callable symbols will be those functions exported using a
+> cgo //export comment. Requires exactly one main package to be listed.
+
+Example:
+
+src/go/main.go:
+
+```go
+package main
+
+import "C"
+import "fmt"
+
+//export helloLib
+func helloLib(x C.int) {
+    fmt.Printf("Hello from Go! x=%d\n", x)
+}
+
+func main() {}
+```
+
+src/c/main.c:
+
+```c
+void helloLib(int);
+
+int main() {
+    helloLib(12345);
+}
+```
+
+Building and running:
+
+```bash
+go build -buildmode=c-shared -o libmy.so ./src/go/
+gcc -o test src/c/main.c libmy.so
+./test
+Hello from Go! x=12345
+```
+
+Sources:
+
+- <https://stackoverflow.com/questions/75035609/can-go-executable-be-used-as-a-dynamic-library>
+- <https://pkg.go.dev/cmd/go#hdr-Build_modes>
+
+## List of languages that has support for FFI with C