Naming Conventions: OCCT vs OCCTSwift

OCCTSwift translates OCCT’s C++ API into idiomatic Swift. This document explains the naming conventions and how they map to the underlying OCCT classes.

Class Hierarchy → Flat Swift Types

OCCT organizes classes by toolkit and module prefix:

The API_Make* builder pattern is replaced by static factory methods on the result type. The toolkit prefix (BRepPrimAPI_, GeomAPI_, etc.) is dropped entirely.

Constructors → Static Factories

OCCT uses constructors with IsDone() guards:

BRepPrimAPI_MakeBox builder(10, 20, 30);
if (builder.IsDone()) {
    TopoDS_Shape s = builder.Shape();
}

OCCTSwift returns optionals — nil replaces the IsDone() check:

let box = Shape.box(width: 10, height: 20, depth: 30)  // Shape?

Verb Tense — Past Participle for Transformations

OCCT uses imperative verbs (Build(), Perform(), Transform()). OCCTSwift follows Swift API Design Guidelines — methods that return a new value use the -ed/-ing suffix:

Named Parameters

OCCT passes positional arguments:

BRepPrimAPI_MakeCylinder(5.0, 10.0);
BRepPrimAPI_MakeCone(5.0, 2.0, 10.0);

OCCTSwift uses Swift labeled arguments throughout:

Shape.cylinder(radius: 5, height: 10)
Shape.cone(bottomRadius: 5, topRadius: 2, height: 10)

Boolean Operations

OCCT has one class per operation:

BRepAlgoAPI_Fuse     → shape.union(with:)
BRepAlgoAPI_Common   → shape.intersection(with:)
BRepAlgoAPI_Cut      → shape.subtracting(_:)
BRepAlgoAPI_Section  → shape.section(with:)

Enums — No Prefix Repetition

OCCT repeats the namespace in every enum value:

TopAbs_SOLID, TopAbs_FACE, TopAbs_EDGE, TopAbs_VERTEX
GeomAbs_C0, GeomAbs_C1, GeomAbs_G1

OCCTSwift uses Swift-style dot-syntax with lowercase cases:

ShapeType.solid, .face, .edge, .vertex
GeometricContinuity.c0, .c1, .g1

Properties vs Query Methods

OCCT uses methods for all queries, even trivial ones:

GProp_GProps props;
BRepGProp::VolumeProperties(shape, props);
double vol = props.Mass();
gp_Pnt com = props.CentreOfMass();

OCCTSwift uses computed properties for zero-argument queries:

shape.volume           // Double?
shape.surfaceArea      // Double?
shape.centerOfMass     // SIMD3<Double>?
shape.bounds           // (min: SIMD3<Double>, max: SIMD3<Double>)
shape.isValid          // Bool

Geometric Types — simd Instead of gp_*

OCCT has its own geometric primitives:

gp_Pnt(1.0, 2.0, 3.0)    // point
gp_Vec(0.0, 0.0, 1.0)     // vector
gp_Dir(0.0, 0.0, 1.0)     // unit direction
gp_Pnt2d(1.0, 2.0)        // 2D point

OCCTSwift uses Swift’s simd types:

SIMD3<Double>(1, 2, 3)     // points, vectors, directions
SIMD2<Double>(1, 2)         // 2D points

Iterators → Arrays

OCCT uses Init/More/Next iterator patterns:

TopExp_Explorer ex(shape, TopAbs_FACE);
for (; ex.More(); ex.Next()) {
    TopoDS_Face f = TopoDS::Face(ex.Current());
}

OCCTSwift returns Swift arrays:

shape.subShapes(ofType: .face)   // [Shape]
shape.vertices()                  // [SIMD3<Double>]
shape.edges()                     // [Edge]

Error Handling

OCCT throws C++ exceptions:

try {
    BRepPrimAPI_MakeBox builder(0, 0, 0);  // degenerate
    TopoDS_Shape s = builder.Shape();
} catch (StdFail_NotDone&) { ... }

OCCTSwift maps errors to:

• nil — geometry operations that can fail cleanly (boolean ops, fillets, etc.)
• throws — I/O operations (Shape.load(from:), Exporter.writeSTEP(shape:to:))

Bridge Layer Naming

The C bridge functions (in OCCTBridge.h / OCCTBridge.mm) follow their own conventions:

The bridge prefixes the handle type (OCCTShape, OCCTWire, OCCTFace, OCCTEdge, OCCTMesh, OCCTCurve3D, OCCTSurface) followed by the operation name. Every Create/Make function has a matching Release function.

Summary