Principle:LaurentMazare Tch rs Crate Organization

Knowledge Sources	LaurentMazare_Tch_rs
Domains	Software Engineering, Module Systems, API Design
Last Updated	2026-02-08 00:00 GMT

Overview

Hierarchical module organization with public re-exports at the root provides flat, ergonomic import paths while maintaining a clean internal structure and optional feature gating.

Description

A well-organized library module hierarchy balances two competing goals: internal organization (grouping related functionality into coherent submodules) and external ergonomics (providing short, intuitive import paths for consumers). The standard approach is to organize code into logically distinct internal modules, then re-export key types and functions at the crate root so users do not need to know the internal structure.

The crate root acts as the public API surface. By selectively re-exporting items from internal modules, the library author controls what is part of the stable API versus what is an implementation detail. This enables refactoring internal structure without breaking downstream consumers, as long as the root-level re-exports remain stable.

Feature gates provide conditional compilation of optional capabilities. Each feature corresponds to a named flag that consumers can enable or disable. Code behind a feature gate is only compiled when that feature is activated, keeping the default build lean and avoiding unnecessary dependencies. Common uses include:

Optional hardware acceleration backends
Python interoperability support
Additional data format support
Experimental or unstable APIs

The module hierarchy typically groups functionality by concern: core tensor operations, neural network building blocks, optimization algorithms, data loading, and serialization. Each group forms a submodule with its own internal organization.

Usage

Apply this organizational principle when:

Building a library with many types and functions that need a coherent public API
Internal structure should be refactorable without API breakage
Optional features should not impose compile-time or dependency costs on all users
Users should be able to import commonly used items with short paths

Theoretical Basis

Module Hierarchy

A module tree can be modeled as a rooted tree where each node represents a module and edges represent containment:

$M = (V, E, r)$

where $V$ is the set of modules, $E$ are parent-child relationships, and $r$ is the root module.

Visibility and Re-exports

Each item $i$ has a visibility scope $v (i) \subseteq V$ . A re-export at the root $r$ extends an item's effective path:

If item $i$ lives at path $r : : a : : b : : i$ and is re-exported at $r$ , then the item is accessible as both $r : : a : : b : : i$ and $r : : i$ .

Feature Gating

Feature gates define a set of boolean flags $F = {f_{1}, f_{2}, \dots, f_{k}}$ . Each code item may be annotated with a predicate over features:

$compiled (i) ⟺ predicate (F, i) = true$

This enables the final compiled artifact to include only the subset of code relevant to the activated features, reducing binary size and compile time.

Facade Pattern

The re-export pattern is an instance of the facade pattern from software design: a simplified interface that hides the complexity of a subsystem. The root module acts as the facade, presenting a curated view of the library's capabilities.

Related Pages

Implementation:LaurentMazare_Tch_rs_Crate_Root

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