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Variants (A | B | ...)

A Variant is a type of either one of the values defined in it's declaration. Example:

interface Math extends HybridObject<{ … }> {
  distance(value: number | Point): number
}
tip

While variants are still very efficient, they need runtime-checks for type conversions, which comes with a tiny overhead compared to all other statically defined types. If possible, avoid variants.

No literal values​

A variant can only consist of types, not of literal values.

export interface Person extends HybridObject<{ … }> {
  getGender(): 'male' | 'female'
}

If you need variants of literal values, you probably want to use an enum (union) instead.

Custom Alias Names​

Each variant is a unique type in Swift/Kotlin - for example: string | number becomes Variant_String_Double.

Since the generated names are hard to read, it is recommended to declare type-aliases with custom names instead:

Bad ❌

interface Math extends HybridObject<{ … }> {
  calculate(): string | number
}
Good ✅
type MathOutput = string | number
interface Math extends HybridObject<{ … }> {
  calculate(): MathOutput
}

This will then use the easier-to-read type-alias name instead of Variant_String_Double:

nitrogen/generated/ios/HybridMathSpec.swift
public protocol HybridMathSpec: HybridObject {
  func calculate() -> Variant_String_Double
  func calculate() -> MathOutput
}