interface-factory-pattern

A software design pattern that exposes interfaces and factory functions while keeping the implementation classes private.

In plain words
What is it for?
Use it when designing reusable services or libraries, especially when callers should depend on what a component does rather than how it is built.
Why use it?
It keeps the public API stable when internal code changes and makes components easier to replace in tests.

Cursor rule for Codex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/prisma/orm/interface-factory-pattern
Clone the repo
git clone --depth 1 https://github.com/prisma/orm

Made for: Codex.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 207 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00000 $0.00207
Opus 5 $0.00000 $0.00103
Sonnet 5 $0.00000 $0.00041
Haiku 4.5 $0.00000 $0.00021

Measured yesterday against content hash 4e2401e3ac7c, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

interface-factory-pattern scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

.agents/rules/interface-factory-pattern.mdc · 43 lines

What it actually says

Interface-Based Design with Factory Functions

Pattern: Export interfaces and factory functions. Keep classes as private implementation details.

Do

export interface CodecRegistry {
  get(id: string): unknown | undefined;
  register(codec: unknown): void;
}

export function createCodecRegistry(): CodecRegistry {
  return new CodecRegistryImpl();
}

class CodecRegistryImpl implements CodecRegistry {
  // ...
}

Avoid

// Avoid exporting concrete classes as the primary surface.
export class CodecRegistry {
  // ...
}

Why this matters

  • Keeps public APIs stable while allowing private implementation changes
  • Makes mocking/testing easier (tests can target interfaces)
  • Encourages “thin core, fat targets” and clean layering
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 43 lines · 0 tokens per session scan A 4e2401e3ac7c

Subscribe to this mod's changes

interface-factory-pattern is a cursor rule published in the GitHub repository prisma/orm (47,579 stars, last pushed today), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 207 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.