[dbohdan] 2016-09-21: The following is an example of how to implement a simple [extension%|%Tcl extension] in [Swift] 3.0 under Linux.

This code has been tested with Apple's official Swift 3.0-RELEASE on Ubuntu 14.04. You can install Swift by following https://vapor.github.io/documentation/getting-started/install-swift-3-ubuntu.html%|%these instructions%|%. If you copy and paste the makefile from the wiki be sure to replace the leading spaces with tabs with the command `sed -i 's|        |\t|' Makefile`.

Note the use of `@_cdecl`: when Tcl loads the shared library `libfoo.so` it looks for the symbol `Foo_Init` in it but since Swift https://mikeash.com/pyblog/friday-qa-2014-08-15-swift-name-mangling.html%|%mangles names%|% and has http://lists.llvm.org/pipermail/llvm-dev/2016-March/096250.html%|%its own calling convention%|% you can't simply write `public func Foo_Init ...` and have the Tcl interpreter find it. You need to annotate the function with `@_cdecl("Foo_Init")`, new in Swift 3.0, to expose it to C code under the symbol name `Foo_Init` with the C calling convention for the platform.


** Makefile **

======none
TARGET ?= libtclswiftexample.so

test: $(TARGET) bridge.h
        echo 'load $(TARGET); puts [hello]; puts [square 5]' | tclsh
$(TARGET): example.swift
        swiftc -emit-library -import-objc-header bridge.h $< -o $(TARGET)
clean:
        -rm $(TARGET)
.PHONY: clean test

======


** bridge.h **

======c
#include "/usr/include/tcl/tcl.h"

======


** example.swift **

======c
func Hello_Cmd(cdata: ClientData?,
               interp: UnsafeMutablePointer<Tcl_Interp>?,
               objc: Int32,
               objv: UnsafePointer<UnsafeMutablePointer<Tcl_Obj>?>?) -> Int32 {
    if objc != 1 {
        Tcl_WrongNumArgs(interp, 1, objv, nil)
        return TCL_ERROR
    }
    Tcl_SetObjResult(interp, Tcl_NewStringObj("Hello, World!", -1))
    return TCL_OK
}

func Square_Cmd(cdata: ClientData?,
                interp: UnsafeMutablePointer<Tcl_Interp>?,
                objc: Int32,
                objv: UnsafePointer<UnsafeMutablePointer<Tcl_Obj>?>?) -> Int32 {
    if objc != 2 {
        Tcl_WrongNumArgs(interp, 1, objv, "value")
        return TCL_ERROR
    }
    var i: Int32 = 0
    if Tcl_GetIntFromObj(interp, objv![1], &i) != TCL_OK {
        return TCL_ERROR
    }
    Tcl_SetObjResult(interp, Tcl_NewIntObj(i*i))
    return TCL_OK
}

@_cdecl("Tclswiftexample_Init")
public func Tclswiftexample_Init(interp: UnsafeMutablePointer<Tcl_Interp>) -> Int32 {
    Tcl_CreateObjCommand(interp, "::hello", Hello_Cmd, nil, nil);
    Tcl_CreateObjCommand(interp, "::square", Square_Cmd, nil, nil);
    return TCL_OK
}

======


** See also **

   * [swift-tcl]

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