Special thanks to Finn Voorhees for swift-switch-examples, which helped provide a reference point for what changes needed to be made to makefiles in order to compile. Thanks also to Ben Barham of the Swift.org forums for instructions on how to configure the SourceKit-LSP for completion and syntax-highlighting in non-SwiftPM projects.

 

Interdimensional Swift

It's Swift... on the Nintendo 3DS!

Do you want to get started with 3DS homebrew, but find C displeasurable? Have you thought to yourself "Gee, I wish there was a language that was easier to understand!"

...Well then, look no further, because this mad goat has just the setup for you! With the power of Embedded Swift, you too can code in Swift for your Nintendo 3DS!

 

Getting Started

1. Set up your development environment

• This guide assumes you have followed the instructions to set up devkitPro, & the 3DS SDK.
  • You can find the instructions to get started with this here: https://devkitpro.org/wiki/Getting_Started
  • Be sure to install all of 3DS-dev via dkp-pacman
  • Make sure DEVKITARM & DEVKITPRO are exported to your system environment variables, either via the relevant shell rc file, or via system settings
• This guide assumes you are using a makefile as your build method of choice.
• This guide assumes you have already installed the latest Swift toolchain for non-Darwin & Embedded development and set it as the default toolchain
• This guide assumes you are using an editor preconfigured to use SourceKit-LSP, the language server for code completion with Swift, such as VSCode with the Swift extension.
• This guide is based off using the DevkitPro 3DS example "Hello-World" (examples/3DS/graphics/printing/hello-world)

 

2. Set up your project layout as follows...

• Project/ ← Root Project Folder
  • source/ ← Source Folder
    • game.swift ← Your main swift file
    • Bridging-Header.h ← The header used to import the 3DS SDK into swift
  • makefile ← Your Makefile
  • compile_commands.json ← The compilation database used to tell the language server to import the header above

Note

Without compile_commands.json, you cannot use Intellisense, or similar code-completion/error-checking/documentation features of your IDE of choice, within your .swift code. Since this is not a Swift Package Manager project, this file essentially tells the Swift language server, SourceKit-LSP, how to import the Bridging-Header which imports the 3DS SDK.

 

3. Configure your Bridging-Header.h as follows...

#include <stdio.h>
#include <3ds.h>
// Any other C headers you need to import go here
// #include <header.h> = header as part of an imported directory at build time
// #include "path/to/header.h" = static path to header not imported by directory

 

4. Configure your compile_commands.json as follows...

[
    {
      "directory": "<ABSOLUTE PATH TO PROJECT ROOT>",
      "command": "swiftc source/game.swift -parse-as-library -enable-experimental-feature Embedded -target armv6-none-none-eabi -no-allocations -import-objc-header source/Bridging-Header.h -I <ABSOLUTE PATH TO DEVKITARM>/include -I <ABSOLUTE PATH TO DEVKITARM>/arm-none-eabi/include -I <ABSOLUTE PATH TO DEVKITPRO>/libctru/include <ANY OTHER INCLUDES AND SWIFT COMPILER FLAGS>",
      "file": "source/game.swift"
    }
]

Important

On POSIX systems (macOS/UNIX, Linux), open the terminal and run echo $DEVKITPRO for the absoslute path to the devkitPro directory, and echo $DEVKITARM for the path to the devkitARM directory. Replace <ABSOLUTE PATH TO DEVKITPRO> and <ABSOLUTE PATH TO DEVKITARM> respectively.

Note

Replace <ANY OTHER INCLUDES AND SWIFT COMPILER FLAGS> with any additional flags and include operations. If none are needed, delete this and the preceding space.

 

5. Alter your makefile as follows...

1. Alter the compiler flags for swift:

- CFLAGS	:=	-g -Wall -O2 -mword-relocations \
+ SWIFTCFLAGS	:=	-g -Wall -O2 \
  		-ffunction-sections \
  		$(ARCH)

- CFLAGS	+=	$(INCLUDE) -D__3DS__
+ SWIFTCFLAGS	+=	$(INCLUDE) -D__3DS__

+ CFLAGS	:=	$(SWIFTCFLAGS) -mword-relocations

Warning

I am not certain how correct this is. -mword-relocations is not a valid flag with the swift compiler, so I am unsure as to how important this may be. For what it is worth, I was able to successfully build and run hello-world with -mword-relocations simply removed, but to err with caution, I have elected to instruct others to instead alter the compilation flags so that Swift effectively receives a variation of CFLAGS with -mword-relocations removed.

2. Add Swift compiler instructions:

#---------------------------------------------------------------------------------
# list of directories containing libraries, this must be the top level containing
# include and lib
#---------------------------------------------------------------------------------
LIBDIRS	:= $(CTRULIB)

+ #---------------------------------------------------------------------------------
+ # Instructions for the Swift compiler
+ #---------------------------------------------------------------------------------
+ SWIFTC := <PATH TO swiftc BINARY>
+ SWIFTFLAGS := -wmo -parse-as-library -enable-experimental-feature Embedded -target armv6-none-none-eabi -no-allocations -import-objc-header ../$(SOURCES)/Bridging-Header.h -I $(DEVKITARM)/include -I $(DEVKITARM)/arm-none-eabi/include -I $(DEVKITPRO)/libctru/include <ANY OTHER INCLUDES OR SWIFT COMPILER FLAGS GO HERE>
+ %.o: %.swift
+ 	@echo $(notdir $<)
+ 	$(ADD_COMPILE_COMMAND) add $(SWIFTC) $(SWIFTFLAGS) "$(addprefix -Xcc , $(C_FLAGS)) -c $< -o $@" $<
+ 	$(SILENTCMD)$(SWIFTC) $(SWIFTFLAGS) $(addprefix -Xcc , $(SWIFTCFLAGS)) -c $< -o $@ $(ERROR_FILTER)

Important

Replace <PATH TO swiftc BINARY> with the absolute path to where swiftc is located. On macOS, this is likely to be /Library/Developer/Toolchains/swift-latest.xctoolchain/usr/bin/swiftc, but if you are using a different toolchain other than latest, YMMV.

Note

Replace <ANY OTHER INCLUDES OR SWIFT COMPILER FLAGS GO HERE> with any additional flags and include operations. If none are needed, delete this and the preceding space.

3. Include .swift files as part of compilation:

export DEPSDIR	:=	$(CURDIR)/$(BUILD)

CFILES		:=	$(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.c)))
+ SWIFTFILES	:=	$(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.swift)))

4. Alter the OFILES_SOURCES to include swift files:

- export OFILES_SOURCES 	:=	$(CPPFILES:.cpp=.o) $(CFILES:.c=.o) $(SFILES:.s=.o)
+ export OFILES_SOURCES 	:=	$(CPPFILES:.cpp=.o) $(CFILES:.c=.o) $(SFILES:.s=.o) $(SWIFTFILES:.swift=.o)

 

6. Write your swift code...

• Example (game.wift):

@main
struct Game {
    static func main() {
        gfxInitDefault()
        
        consoleInit(GFX_TOP, nil)

    	print("Hello from Swift!")
	print("Press B to exit.")

        while(aptMainLoop()) {
            hidScanInput()
            var kDown: UInt32 = hidKeysDown()

            if (kDown == KEY_B) { 
                break // break in order to return to hbmenu
            }

		// Flush and swap framebuffers
		gfxFlushBuffers()
		gfxSwapBuffers()

		//Wait for VBlank
		gspWaitForEvent(GSPGPU_EVENT_VBlank0, true)

        }
        gfxExit()
    }
}

 

7. make, and enjoy! :)