Type Parameters

Type Parameter Naming

Convention

• Type aliases and interfaces: Use $ prefix

  • type Transform<$Input> = $Input extends string ? number : boolean
  • interface Container<$T> { value: $T }

• Functions and methods: Use $ prefix matching the value parameter name

  • function process<$value>(value: $value): $value
  • function map<$item, $result>(item: $item, fn: ($item) => $result): $result

• Type guard exception: Add _ suffix to avoid conflict with narrowed type

  • function isString<$value_>(value: unknown): value is $value_

• Generic returns exception: When type param is NOT mapped to value parameter

  • function create<$T>(): $T

• Utility internals: Parameters with ___ prefix are implementation details

  • type Utility<$T, ___Internal = SomeDefault<$T>> = ...

• Mapped types: Use specific single-letter iterators

  • Objects: k (key) - { [k in keyof $T]: $T[k] }
  • Tuples/arrays: i (index) - { [i in keyof $T]: Transform<$T[i]> }

• Infer clauses: Use __lowercase__ pattern

  • $T extends Array<infer __element__> ? __element__ : never

Type Parameter Defaults

Default type parameters to their widest possible variant:

// GOOD - Defaults to widest
type ParserContext<
  $Schema = Schema | undefined,
  $SDDM = any,
  $TypeHooks = never
> = ...

// Usage with clean constraints
function parse<$Context extends ParserContext>(...) // Clean!

// BAD - Cluttered constraint
function parse<$Context extends ParserContext<any, any, any>>(...) // Ugly!