template

import type {
  TrimLeft, TrimRight, Trim,
  CapitalizeWords, SnakeToCamel,
} from '@gentleduck/ttest/template'

String-shape transforms expressed as type-level recursion on template literals. The companion to object *CaseKeys — these operate on a single string, those operate on every key of an object.

TrimLeft

type TrimLeft<S extends string>

Strip leading whitespace (space, newline, tab).

type a = TrimLeft<'  hello'>   // 'hello'
type b = TrimLeft<'\n\thello'> // 'hello'
type c = TrimLeft<'hello'>     // 'hello'

TrimRight

type TrimRight<S extends string>

Strip trailing whitespace.

type a = TrimRight<'hello   '>   // 'hello'
type b = TrimRight<'hello\n'>    // 'hello'

Trim

type Trim<S extends string> = TrimLeft<TrimRight<S>>

Strip both sides.

type a = Trim<'  hello  '>           // 'hello'
type b = Trim<'\n  hello world  \t'> // 'hello world'

Edge case: Trim<string> is string. Whitespace stripping only narrows literal types — a wide string passes through unchanged.

CapitalizeWords

type CapitalizeWords<S extends string>

Capitalize each space-separated word; lowercase the rest. Useful for headers, button labels, and titles authored as identifiers.

type a = CapitalizeWords<'hello WORLD'>     // 'Hello World'
type b = CapitalizeWords<'order details'>   // 'Order Details'
type c = CapitalizeWords<'mixedCASEinput'>  // 'Mixedcaseinput'

Edge case: the transform splits on a single space character only. Tabs and multiple spaces leave the residue inside a "word".

SnakeToCamel

type SnakeToCamel<S extends string>

Convert snake_case to camelCase by removing underscores and capitalizing the character that follows.

type a = SnakeToCamel<'user_name'>           // 'userName'
type b = SnakeToCamel<'first_name_initial'>  // 'firstNameInitial'
type c = SnakeToCamel<'already_camel'>       // 'alreadyCamel'
type d = SnakeToCamel<'noUnderscores'>       // 'noUnderscores'

Edge cases:

• SnakeToCamel<'__double__'> produces 'Double_' — the helper assumes single underscores.
• SnakeToCamel<string> is string — wide strings pass through.

For object-key case conversion at scale see object — CamelCaseKeys, SnakeCaseKeys, and their deep variants build on these primitives.