gox.mod is the module configuration file for XGo (formerly known as Go+). It belongs to class framework packages — not to ordinary XGo application projects. Its role is analogous to a plugin manifest: it tells the XGo toolchain how a given framework's class system is structured, what file extensions map to which class types, and which packages should be auto-imported.

Note: Ordinary XGo projects do not need a gox.mod file. They use a standard go.mod file, just like any Go project. gox.mod only lives inside class framework packages themselves.

Legacy alias: In older versions of XGo, this file was named gop.mod. The gop directive is still accepted for backward compatibility.

When you run xgo run (or xgo build, xgo install, xgo test, etc.) on a project, XGo does not look for a gox.mod in your project directory. Instead, it follows this discovery process:

XGo reads your project's go.mod and inspects every require entry for an //xgo:class annotation:

require (
    github.com/goplus/spx/v2 v2.0.0 //xgo:class
    github.com/goplus/yap v0.8.0 //xgo:class
)

Any dependency annotated with //xgo:class is recognized as a class framework.

For each identified class framework, XGo locates the corresponding gox.mod file from the framework package — either from the local module cache or a local replace path.

XGo parses the gox.mod to learn:

• Which file extension patterns map to which project class (e.g. main.spx → Game)
• Which file extension patterns map to which work class (e.g. *.spx → SpriteImpl)
• Which packages should be auto-imported into every source file

Armed with the file glob patterns from gox.mod, the xgo/parser package knows exactly which files to treat as which class type and parses them accordingly.

This design means your project stays clean — just a go.mod and your source files. All the class system configuration is owned and versioned by the framework package itself.

A gox.mod file is composed of a small set of directives. Each directive occupies one line (or a line block). The supported directives are:

xgo <version>

Specifies the minimum XGo language version required by this module. The version must follow the 1.x or 1.x.y format.

Example:

xgo 1.6.0

The directive was historically also written as gop and is still accepted under that name.

project [*.projExt ProjectClass] classFilePkgPath ...

Declares a classfile project. A project defines the entry-point file extension, the Go class that represents the project, and one or more Go package paths that implement the classfile framework.

Arguments:

Examples:

# Project with extension and class
project main.spx Game github.com/goplus/spx/v2 math
 
# Project with package path only (no dedicated entry file)
project github.com/example/myframework

Extension formats:

The project extension (*.projExt) can be expressed in several forms:

class [-embed] [-prefix=Prefix] *.workExt WorkClass [WorkPrototype]

Declares a work class within the most recently declared project. A work class represents the individual actor or object type (e.g. a sprite in a game) that operates within the project. Multiple class directives can follow a single project.

Flags:

Arguments:

Example:

class -embed *.spx SpriteImpl

This declares that every *.spx file (other than the project entry file) is compiled as a SpriteImpl work class, and that the class instance is embedded into the project.

import [name] pkgPath

Declares a package to be automatically imported into every source file of the current project. This allows classfile frameworks to inject utility packages transparently.

Arguments:

Example:

project .yap YapApp github.com/goplus/yap
 
import "github.com/goplus/yap/test"

The following is the gox.mod configuration for the spx classfile framework, which powers XGo's 2D game programming environment:

xgo 1.6.0
 
project main.spx Game github.com/goplus/spx/v2 math
 
class -embed *.spx SpriteImpl

1. xgo 1.6.0 — This module requires XGo version 1.6.0 or later.

2. project main.spx Game github.com/goplus/spx/v2 math

   • The file main.spx is the project entry point.
   • It is compiled as a Game class (from github.com/goplus/spx/v2).
   • The math standard library package is also part of the classfile's package set.

3. class -embed *.spx SpriteImpl

   • Every other *.spx file in the project (i.e., files that are not main.spx) is compiled as a SpriteImpl work class.
   • The -embed flag means each sprite instance is embedded directly into the Game project struct, enabling direct method calls between the game and its sprites.

An application project built on spx does not have a gox.mod. It has a go.mod that references the framework with the //xgo:class annotation:

module mygame
 
go 1.21
 
require github.com/goplus/spx/v2 v2.0.0 //xgo:class

When xgo run is invoked, it reads this annotation, finds spx/v2's gox.mod, and learns that main.spx files are Game instances and all other *.spx files are SpriteImpl instances.

mygame/
├── go.mod          # standard Go module file (no gox.mod needed here)
├── main.spx        # project file → compiled as Game
├── Cat.spx         # work file → compiled as SpriteImpl
└── Dog.spx         # work file → compiled as SpriteImpl

gox.mod is the heart of XGo's classfile system, but it lives in framework packages, not in user projects. Ordinary XGo projects use a plain go.mod with //xgo:class annotations on their framework dependencies — that's the signal xgo run and other toolchain commands use to discover the relevant gox.mod files and learn the class structure (file patterns, class types, auto-imports) before parsing and compiling the project's source files.

By combining a handful of expressive directives — project, class, and import — framework authors can define rich, type-safe, domain-specific programming environments (games, web servers, data pipelines, etc.) that XGo source files compile into directly, without any boilerplate.