Discriminated Unions

The SDKs natively support discriminated unions for both OpenAPI and Fern APIs.

Fern Definition

OpenAPI Specification

TypeScript

Go

1 export type Shape = Triangle | Square;
2 
3 export interface Triangle {
4   type: "triangle";
5   a: number;
6   b: number;
7   c: number;
8 }
9 
10 export interface Square {
11   type: "square";
12   side: number;
13 }

Callers can create a Shape object by simply constructing the appropriate type. For example, creating a Triangle shape looks like the following:

1 const shape: Shape = {
2   type: "triangle",
3   a: 3,
4   b: 4,
5   c: 5,
6 };

Consumers can easily write branching logic by checking the discriminant.

1 import { Shape } from "sdk";
2 
3 export function computeArea(shape: Shape): number {
4   if (shape.type === "triangle") {
5     // compute triangle area
6   } else if (shape.type === "square") {
7     // compute square area
8   }
9 }

1	export type Shape = Triangle \| Square;
2
3	export interface Triangle {
4	type: "triangle";
5	a: number;
6	b: number;
7	c: number;
8	}
9
10	export interface Square {
11	type: "square";
12	side: number;
13	}

1	const shape: Shape = {
2	type: "triangle",
3	a: 3,
4	b: 4,
5	c: 5,
6	};

1	import { Shape } from "sdk";
2
3	export function computeArea(shape: Shape): number {
4	if (shape.type === "triangle") {
5	// compute triangle area
6	} else if (shape.type === "square") {
7	// compute square area
8	}
9	}