dbohdan 2016-09-19: The following is, to my best knowledge, about as simple as a Tcl extension written in Go can get. The wrapper functions are necessary since you can't pass a pointer to a Go function to C code. In a real extension those wrappers could be generated automatically. The code has been tested with Go v1.6.3 on Linux x86_64. Build and run with gmake test.
libtclgoexample.so: *.go go build -o $@ -buildmode=c-shared test: libtclgoexample.so echo 'load libtclgoexample.so; puts [hello]; puts [square 5]' | tclsh .PHONY: test
//example.go package main /* #include <stdlib.h> #include <tcl.h> #include <tclDecls.h> #cgo LDFLAGS: -ltcl8.6 int Hello_Cmd_cgo(ClientData cdata, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[]); int Square_Cmd_cgo(ClientData cdata, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[]); */ import "C" import ( "reflect" "strconv" "unsafe" ) const ( TCL_OK = 0 TCL_ERROR = 1 TCL_RETURN = 2 TCL_BREAK = 3 TCL_CONTINUE = 4 ) //export Hello_Cmd func Hello_Cmd(cdata C.ClientData, interp *C.struct_Tcl_Interp, objc C.int, objv **C.Tcl_Obj) C.int { if objc != 1 { return TCL_ERROR } result := C.CString("Hello, World!") defer C.free(unsafe.Pointer(result)) C.Tcl_SetObjResult(interp, C.Tcl_NewStringObj(result, -1)) return TCL_OK } //export Square_Cmd func Square_Cmd(cdata C.ClientData, interp *C.struct_Tcl_Interp, objc C.int, objv **C.Tcl_Obj) C.int { if objc != 2 { return TCL_ERROR } // http://stackoverflow.com/a/14828189 var objs []*C.Tcl_Obj sliceHeader := (*reflect.SliceHeader)((unsafe.Pointer(&objs))) sliceHeader.Cap = (int)(objc) sliceHeader.Len = (int)(objc) sliceHeader.Data = uintptr(unsafe.Pointer(objv)) arg := C.GoString(C.Tcl_GetString(objs[1])) i, err := strconv.Atoi(arg) if err != nil { return TCL_ERROR } C.Tcl_SetObjResult(interp, C.Tcl_NewIntObj((C.int)(i*i))) return TCL_OK } func (interp *C.struct_Tcl_Interp) createCommand(name string, f unsafe.Pointer) { cname := C.CString(name) defer C.free(unsafe.Pointer(cname)) C.Tcl_CreateObjCommand(interp, cname, (*C.Tcl_ObjCmdProc)(f), nil, nil) } //export Tclgoexample_Init func Tclgoexample_Init(interp *C.struct_Tcl_Interp) C.int { interp.createCommand("::hello", unsafe.Pointer(C.Hello_Cmd_cgo)) interp.createCommand("::square", unsafe.Pointer(C.Square_Cmd_cgo)) return TCL_OK } func main() {}
//wrappers.go package main /* #include <tcl.h> #include <tclDecls.h> int Hello_Cmd_cgo(ClientData cdata, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[]) { int Hello_Cmd(ClientData cdata, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[]); return Hello_Cmd(cdata, interp, objc, objv); } int Square_Cmd_cgo(ClientData cdata, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[]) { int Square_Cmd(ClientData cdata, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[]); return Square_Cmd(cdata, interp, objc, objv); } */ import "C"