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 *_cgo 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 via go generate and a Tcl script.
The code has been tested with Go v1.6.3 on Linux x86_64. To build it yourself save example.go, wrappers.go and Makefile in the same directory, replace the spaces with tabs with
$ sed 's/ /\t/g' -i example.go wrappers.go Makefile
which is necessary for the Makefile to work, then run make test.
libtclgoexample.so: example.go wrappers.go
go build -o $@ -buildmode=c-shared example.go wrappers.go
test: libtclgoexample.so
echo 'load libtclgoexample.so; puts [hello]; puts [square 5]' | tclsh
.PHONY: test//example.go v0.2.0
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"
"unsafe"
)
const (
TCL_OK = 0
TCL_ERROR = 1
TCL_RETURN = 2
TCL_BREAK = 3
TCL_CONTINUE = 4
)
func (interp *C.struct_Tcl_Interp) createCommand(name string,
f *C.Tcl_ObjCmdProc) {
cName := C.CString(name)
defer C.free(unsafe.Pointer(cName))
C.Tcl_CreateObjCommand(interp, cName, f, nil, nil)
}
func (interp *C.struct_Tcl_Interp) wrongNumArgs(objc C.int,
objv **C.Tcl_Obj, message string) {
var cMessage *C.char
if message == "" {
cMessage = nil
} else {
cMessage = C.CString(message)
defer C.free(unsafe.Pointer(cMessage))
}
C.Tcl_WrongNumArgs(interp, objc, objv, cMessage)
}
func slicify(objc C.int, objv **C.Tcl_Obj) (objs []*C.Tcl_Obj) {
// http://stackoverflow.com/a/14828189
sliceHeader := (*reflect.SliceHeader)(unsafe.Pointer(&objs))
sliceHeader.Cap = (int)(objc)
sliceHeader.Len = (int)(objc)
sliceHeader.Data = uintptr(unsafe.Pointer(objv))
return
}
//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 {
interp.wrongNumArgs(1, objv, "")
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 {
interp.wrongNumArgs(1, objv, "value")
return TCL_ERROR
}
objs := slicify(objc, objv)
var i C.int
if C.Tcl_GetIntFromObj(interp, objs[1], &i) != TCL_OK {
return TCL_ERROR
}
C.Tcl_SetObjResult(interp, C.Tcl_NewIntObj((C.int)(i*i)))
return TCL_OK
}
//export Tclgoexample_Init
func Tclgoexample_Init(interp *C.struct_Tcl_Interp) C.int {
interp.createCommand("::hello", (*C.Tcl_ObjCmdProc)(C.Hello_Cmd_cgo))
interp.createCommand("::square", (*C.Tcl_ObjCmdProc)(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"