cthulu

Rationale

Why. A Command has no arguments, and a program launched from a command line has nothing but.

Problem. A launcher that must know how each program reads its arguments can run only the programs it knows.

Solution. Ritual is GoF's two-way ADAPTER: a commander Command that is also an eldritch Invocation, so a launcher executes it and its work asks it for the arguments. FromCommandLine makes one of the arguments a program was launched with.

Key Concepts

Ritual

Role. GoF's two-way ADAPTER, with no members of its own: the Command a launcher executes, and the Invocation its work reads its arguments from and reports progress and complaints to.

Pattern. Adapter

FromCommandLine

Role. A program's reading of its own command line: a Function from the arguments it was launched with to the Ritual they mean.

Pattern. Factory Method

How It Works

Guarantees. FromCommandLine refuses null arguments and never answers a null Ritual.

Thread safety. Cthulu holds no state; a Ritual is as safe as its implementor.

Lane

Purpose. The contract between a launcher and a program launched from a command line.

Alternative. java.util.spi.ToolProvider, when the caller needs an exit status rather than an exception.

Usage

A program says what its arguments mean

public final class MyCommandLine implements FromCommandLine {
    @Override
    public Ritual apply(final String[] arguments) {
        return new MyRun(new MyArguments(arguments));
    }
}

Dependencies

• software.visionary:commander:2026.10.13 at Compile
• software.visionary:eldritch:2026.10.13 at Compile
• software.visionary.contrax:processor:2026.10.13 at Processor

Caveats

• A Ritual refuses by throwing, never by a status; whoever executes it decides what a refusal means. Because complain() promises the run exits 1, a Ritual that complained throws once its work is done.

Views

Drawn from the release. A link in a view opens its source at the release tag.