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Home / Tutorials / 📘 typescript
Part 88 of 355

🔤 Type-Level String Operations: Advanced Manipulations

Master advanced string manipulation at the type level in TypeScript, creating powerful text processing algorithms and compile-time string transformations 🚀

💎Advanced
35 min read

Prerequisites

  • Expert knowledge of template literal types and string manipulation 📝
  • Deep understanding of recursive type patterns and conditional types ⚡
  • Experience with advanced type-level programming techniques 💻

What you'll learn

  • Implement complex string algorithms at the type level 🎯
  • Build text processing and validation systems with types 🏗️
  • Create compile-time parsers and string transformers 🐛
  • Apply advanced string manipulation to real-world problems ✨

🎯 Introduction

Welcome to the linguistic laboratory of TypeScript’s type system! 🔤 This tutorial explores the art and science of advanced string manipulation at the type level, where you’ll learn to build sophisticated text processing algorithms using only TypeScript’s type features.

You’ll discover how to implement complex string operations like parsing, formatting, validation, and transformation entirely at compile time. Whether you’re building template engines 📝, creating DSL parsers 🔍, or implementing advanced string validators 🛡️, type-level string operations provide incredible power for compile-time text processing.

By the end of this tutorial, you’ll be crafting string algorithms that run during compilation and building text processors that guarantee correctness at the type level! Let’s parse the impossible! 🧠

📚 Advanced Template Literal Foundations

🤔 Template Literal Type Mastery

Template literal types are the foundation of all string manipulation at the type level. Let’s explore advanced patterns and techniques:

// 🌟 Advanced template literal patterns
type SimpleTemplate = `Hello, ${string}!`;
type NumberTemplate = `Count: ${number}`;
type BooleanTemplate = `Active: ${boolean}`;

// 🎯 Multi-parameter templates
type ComplexTemplate = `${string}-${number}-${boolean}`;

// ✨ Nested template literals
type NestedTemplate<T extends string> = `Outer[${`Inner[${T}]`}]`;

// 🔄 Conditional template literals
type ConditionalTemplate<T extends string> = 
  T extends "" ? "Empty" : `Non-empty: ${T}`;

// 🧪 Template literal examples
type Example1 = SimpleTemplate; // "Hello, ${string}!"
type Example2 = NestedTemplate<"test">; // "Outer[Inner[test]]"
type Example3 = ConditionalTemplate<"">; // "Empty"
type Example4 = ConditionalTemplate<"hello">; // "Non-empty: hello"

🏗️ String Pattern Matching Infrastructure

// 🎯 Pattern extraction utilities
type ExtractBetween<
  S extends string,
  Start extends string,
  End extends string> = S extends `${string}${Start}${infer Content}${End}${string}` ? Content : never;

type ExtractAfter<S extends string, Delimiter extends string> = 
  S extends `${string}${Delimiter}${infer Rest}` ? Rest : never;

type ExtractBefore<S extends string, Delimiter extends string> = 
  S extends `${infer Before}${Delimiter}${string}` ? Before : never;

// 🔍 Pattern matching examples
type BetweenParens = ExtractBetween<"Hello (world) test", "(", ")">; // "world"
type AfterColon = ExtractAfter<"name:value", ":">; // "value"
type BeforeAt = ExtractBefore<"[email protected]", "@">; // "user"

// 🌟 Advanced pattern matching
type ExtractAllBetween<
  S extends string,
  Start extends string,
  End extends string,
  Acc extends string[] = []
> = S extends `${infer Before}${Start}${infer Content}${End}${infer After}`
  ? ExtractAllBetween<After, Start, End, [...Acc, Content]>
  : Acc;

type AllParens = ExtractAllBetween<"(first) and (second) plus (third)", "(", ")">; 
// ["first", "second", "third"]

// 🔄 String splitting
type Split<S extends string, Delimiter extends string> = 
  S extends `${infer First}${Delimiter}${infer Rest}`
    ? [First, ...Split<Rest, Delimiter>]
    : [S];

type SplitExample = Split<"a,b,c,d", ",">; // ["a", "b", "c", "d"]

// 📊 Character-by-character processing
type ToCharArray<S extends string> = 
  S extends `${infer First}${infer Rest}`
    ? [First, ...ToCharArray<Rest>]
    : [];

type CharArray = ToCharArray<"hello">; // ["h", "e", "l", "l", "o"]

🔤 String Transformation Primitives

// 🎨 Case transformations
type ToUpperCase<S extends string> = Uppercase<S>;
type ToLowerCase<S extends string> = Lowercase<S>;
type ToCapitalize<S extends string> = Capitalize<S>;
type ToUncapitalize<S extends string> = Uncapitalize<S>;

// 🔄 Advanced case transformations
type ToCamelCase<S extends string> = 
  S extends `${infer First}_${infer Rest}`
    ? `${Lowercase<First>}${Capitalize<ToCamelCase<Rest>>}`
    : Lowercase<S>;

type ToPascalCase<S extends string> = Capitalize<ToCamelCase<S>>;

type ToKebabCase<S extends string> = 
  S extends `${infer First}${infer Rest}`
    ? First extends Uppercase<First>
      ? First extends Lowercase<First>
        ? `${First}${ToKebabCase<Rest>}`
        : `${S extends `${string}${First}${string}` ? "-" : ""}${Lowercase<First>}${ToKebabCase<Rest>}`
      : `${First}${ToKebabCase<Rest>}`
    : "";

type ToSnakeCase<S extends string> = 
  S extends `${infer First}${infer Rest}`
    ? First extends Uppercase<First>
      ? First extends Lowercase<First>
        ? `${First}${ToSnakeCase<Rest>}`
        : `${S extends `${string}${First}${string}` ? "_" : ""}${Lowercase<First>}${ToSnakeCase<Rest>}`
      : `${First}${ToSnakeCase<Rest>}`
    : "";

// ✅ Case transformation examples
type CamelTest = ToCamelCase<"hello_world_example">; // "helloWorldExample"
type PascalTest = ToPascalCase<"hello_world_example">; // "HelloWorldExample"
type KebabTest = ToKebabCase<"HelloWorldExample">; // "hello-world-example"
type SnakeTest = ToSnakeCase<"HelloWorldExample">; // "hello_world_example"

// 🎯 String trimming and padding
type TrimLeft<S extends string> = 
  S extends ` ${infer Rest}` ? TrimLeft<Rest> : S;

type TrimRight<S extends string> = 
  S extends `${infer Rest} ` ? TrimRight<Rest> : S;

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

type PadLeft<S extends string, N extends number, Char extends string = " "> = 
  S["length"] extends N ? S : PadLeft<`${Char}${S}`, N, Char>;

type PadRight<S extends string, N extends number, Char extends string = " "> = 
  S["length"] extends N ? S : PadRight<`${S}${Char}`, N, Char>;

// ✅ Trimming and padding examples
type TrimmedLeft = TrimLeft<"   hello">; // "hello"
type TrimmedRight = TrimRight<"hello   ">; // "hello"
type FullyTrimmed = Trim<"  hello  ">; // "hello"

🧮 String Algorithm Implementation

🔍 String Search and Replace

// 🎯 String search algorithms
type Contains<S extends string, Search extends string> = 
  S extends `${string}${Search}${string}` ? true : false;

type StartsWith<S extends string, Prefix extends string> = 
  S extends `${Prefix}${string}` ? true : false;

type EndsWith<S extends string, Suffix extends string> = 
  S extends `${string}${Suffix}` ? true : false;

// 🔄 String replacement
type Replace<
  S extends string, 
  Search extends string, 
  Replace extends string> = S extends `${infer Before}${Search}${infer After}`
  ? `${Before}${Replace}${After}`
  : S;

type ReplaceAll<
  S extends string,
  Search extends string,
  Replace extends string> = S extends `${infer Before}${Search}${infer After}`
  ? `${Before}${Replace}${ReplaceAll<After, Search, Replace>}`
  : S;

// ✅ Search and replace examples
type ContainsTest = Contains<"hello world", "world">; // true
type StartsTest = StartsWith<"TypeScript", "Type">; // true
type EndsTest = EndsWith<"JavaScript", "Script">; // true

type ReplaceTest = Replace<"hello world", "world", "TypeScript">; // "hello TypeScript"
type ReplaceAllTest = ReplaceAll<"foo bar foo", "foo", "baz">; // "baz bar baz"

// 🔍 Advanced search patterns
type FindIndices<
  S extends string,
  Search extends string,
  Index extends number = 0,
  Acc extends number[] = []
> = S extends `${infer First}${infer Rest}`
  ? S extends `${Search}${string}`
    ? FindIndices<Rest, Search, Index, [...Acc, Index]>
    : FindIndices<Rest, Search, Index, Acc>
  : Acc;

// Would be complex to implement with current TS limitations
type IndicesExample = FindIndices<"abcabc", "a">; // Conceptual: [0, 3]

// 🎨 Pattern-based replacement
type ReplacePattern<
  S extends string,
  Pattern extends string,
  Replacement extends string> = S extends `${infer Before}${Pattern}${infer After}`
  ? `${Before}${Replacement}${ReplacePattern<After, Pattern, Replacement>}`
  : S;

type PatternTest = ReplacePattern<"aXbXcXd", "X", "-">; // "a-b-c-d"

📊 String Length and Counting

// 📏 String length calculation
type StringLength<S extends string, Acc extends unknown[] = []> = 
  S extends `${string}${infer Rest}`
    ? StringLength<Rest, [...Acc, unknown]>
    : Acc['length'];

// 🔢 Character counting
type CountChar<
  S extends string,
  Char extends string,
  Count extends unknown[] = []
> = S extends `${infer First}${infer Rest}`
  ? First extends Char
    ? CountChar<Rest, Char, [...Count, unknown]>
    : CountChar<Rest, Char, Count>
  : Count['length'];

// 📈 Word counting
type CountWords<S extends string> = 
  Split<Trim<S>, " "> extends infer Words
    ? Words extends string[]
      ? Words['length']
      : 0
    : 0;

// ✅ Length and counting examples
type LengthTest = StringLength<"hello">; // 5
type CharCountTest = CountChar<"hello", "l">; // 2
type WordCountTest = CountWords<"hello world test">; // 3

// 🎯 Substring operations
type Substring<
  S extends string,
  Start extends number,
  Length extends number = StringLength<S>
> = S extends string ? 
  // Complex implementation would be needed for full substring support
  S : never;

// 🔄 String reversal
type Reverse<S extends string> = 
  S extends `${infer First}${infer Rest}`
    ? `${Reverse<Rest>}${First}`
    : "";

type ReverseTest = Reverse<"hello">; // "olleh"

// 📊 String comparison
type Compare<A extends string, B extends string> = 
  A extends B ? 0 :
  A extends `${B}${string}` ? 1 :
  B extends `${A}${string}` ? -1 :
  // Lexicographic comparison would need char-by-char implementation
  number;

type CompareTest1 = Compare<"abc", "abc">; // 0
type CompareTest2 = Compare<"abcd", "abc">; // 1
type CompareTest3 = Compare<"abc", "abcd">; // -1

📝 Template Engine and Parser Implementation

🏭 Template Variable Substitution

// 🎯 Template variable extraction
type ExtractVariables<T extends string> = 
  T extends `${string}{{${infer Var}}}${infer Rest}`
    ? [Var, ...ExtractVariables<Rest>]
    : [];

type TemplateVars = ExtractVariables<"Hello {{name}}, you have {{count}} messages">; 
// ["name", "count"]

// 🔄 Template substitution
type SubstituteTemplate<
  Template extends string,
  Values extends Record<string, string>
> = Template extends `${infer Before}{{${infer Key}}}${infer After}`
  ? Key extends keyof Values
    ? SubstituteTemplate<`${Before}${Values[Key]}${After}`, Values>
    : SubstituteTemplate<`${Before}{{${Key}}}${After}`, Values>
  : Template;

// ✅ Template substitution example
type TemplateResult = SubstituteTemplate<
  "Hello {{name}}, you have {{count}} messages",
  { name: "Alice"; count: "5" }
>; // "Hello Alice, you have 5 messages"

// 🎨 Advanced template features
type TemplateWithDefaults<
  Template extends string,
  Values extends Record<string, string>,
  Defaults extends Record<string, string> = {}
> = Template extends `${infer Before}{{${infer Key}}}${infer After}`
  ? Key extends keyof Values
    ? TemplateWithDefaults<`${Before}${Values[Key]}${After}`, Values, Defaults>
    : Key extends keyof Defaults
      ? TemplateWithDefaults<`${Before}${Defaults[Key]}${After}`, Values, Defaults>
      : TemplateWithDefaults<`${Before}{{${Key}}}${After}`, Values, Defaults>
  : Template;

type TemplateWithDefaultsResult = TemplateWithDefaults<
  "Hello {{name}}, your role is {{role}}",
  { name: "Bob" },
  { role: "user" }
>; // "Hello Bob, your role is user"

// 🔍 Template validation
type ValidateTemplate<
  Template extends string,
  RequiredVars extends string[]
> = ExtractVariables<Template> extends infer Vars
  ? Vars extends string[]
    ? RequiredVars[number] extends Vars[number]
      ? true
      : false
    : false
  : false;

type ValidTemplate = ValidateTemplate<
  "Hello {{name}}, age {{age}}",
  ["name", "age"]
>; // true

type InvalidTemplate = ValidateTemplate<
  "Hello {{name}}",
  ["name", "age"]
>; // false

🔍 URL and Path Parsing

// 🌐 URL parsing
type ParseURL<URL extends string> = 
  URL extends `${infer Protocol}://${infer Rest}`
    ? Rest extends `${infer Host}/${infer Path}`
      ? {
          protocol: Protocol;
          host: Host;
          path: `/${Path}`;
        }
      : {
          protocol: Protocol;
          host: Rest;
          path: "/";
        }
    : never;

type URLParts = ParseURL<"https://example.com/api/users">; 
// { protocol: "https"; host: "example.com"; path: "/api/users" }

// 🛤️ Path parameter extraction
type ExtractPathParams<Path extends string> = 
  Path extends `${string}:${infer Param}/${infer Rest}`
    ? [Param, ...ExtractPathParams<Rest>]
    : Path extends `${string}:${infer Param}`
      ? [Param]
      : [];

type PathParams = ExtractPathParams<"/users/:id/posts/:postId">; // ["id", "postId"]

// 🎯 Route matching
type MatchRoute<
  Pattern extends string,
  URL extends string> = Pattern extends `${infer PatternStart}:${infer ParamName}/${infer PatternRest}`
  ? URL extends `${infer URLStart}${infer ParamValue}/${infer URLRest}`
    ? PatternStart extends URLStart
      ? MatchRoute<PatternRest, URLRest> extends infer RestMatch
        ? RestMatch extends Record<string, string>
          ? RestMatch & { [K in ParamName]: ParamValue }
          : never
        : never
      : never
    : never
  : Pattern extends `${infer PatternStart}:${infer ParamName}`
    ? URL extends `${infer URLStart}${infer ParamValue}`
      ? PatternStart extends URLStart
        ? { [K in ParamName]: ParamValue }
        : never
      : never
    : Pattern extends URL
      ? {}
      : never;

type RouteMatch = MatchRoute<"/users/:id", "/users/123">; // { id: "123" }

// 🔍 Query string parsing
type ParseQueryString<Query extends string> = 
  Query extends `${infer Key}=${infer Value}&${infer Rest}`
    ? { [K in Key]: Value } & ParseQueryString<Rest>
    : Query extends `${infer Key}=${infer Value}`
      ? { [K in Key]: Value }
      : {};

type QueryParams = ParseQueryString<"name=John&age=30&city=NYC">; 
// { name: "John"; age: "30"; city: "NYC" }

🧮 Expression Parser

// 🎯 Mathematical expression parsing
type ParseNumber<S extends string> = 
  S extends `${infer N}` 
    ? N extends `${number}` 
      ? N 
      : never 
    : never;

type ParseExpression<Expr extends string> = 
  Expr extends `${infer Left} + ${infer Right}`
    ? { type: "addition"; left: ParseExpression<Left>; right: ParseExpression<Right> }
    : Expr extends `${infer Left} - ${infer Right}`
      ? { type: "subtraction"; left: ParseExpression<Left>; right: ParseExpression<Right> }
      : Expr extends `${infer Left} * ${infer Right}`
        ? { type: "multiplication"; left: ParseExpression<Left>; right: ParseExpression<Right> }
        : Expr extends `${infer Left} / ${infer Right}`
          ? { type: "division"; left: ParseExpression<Left>; right: ParseExpression<Right> }
          : ParseNumber<Expr> extends never
            ? { type: "variable"; name: Expr }
            : { type: "number"; value: ParseNumber<Expr> };

type ExpressionAST = ParseExpression<"x + 5">; 
// { type: "addition"; left: { type: "variable"; name: "x" }; right: { type: "number"; value: "5" } }

// 🔄 JSON-like structure parsing
type ParseJSONValue<S extends string> = 
  S extends "true" ? true :
  S extends "false" ? false :
  S extends "null" ? null :
  S extends `"${infer StringValue}"` ? StringValue :
  S extends `${infer NumberValue}` 
    ? NumberValue extends `${number}` 
      ? NumberValue 
      : never 
    : never;

// 📊 CSV parsing
type ParseCSVRow<Row extends string> = 
  Row extends `${infer First},${infer Rest}`
    ? [ParseJSONValue<First>, ...ParseCSVRow<Rest>]
    : [ParseJSONValue<Row>];

type CSVRow = ParseCSVRow<'"John","Doe",30,true'>; 
// ["John", "Doe", "30", true]

🛡️ String Validation and Formatting

📧 Advanced String Validation

// 📧 Email validation
type IsValidEmail<Email extends string> = 
  Email extends `${infer LocalPart}@${infer Domain}`
    ? LocalPart extends ""
      ? false
      : Domain extends `${infer DomainName}.${infer TLD}`
        ? DomainName extends ""
          ? false
          : TLD extends ""
            ? false
            : true
        : false
    : false;

// 📱 Phone number validation
type IsValidPhoneUS<Phone extends string> = 
  Phone extends `+1${infer Rest}`
    ? Rest extends `${infer AreaCode}${infer Exchange}${infer Number}`
      ? StringLength<AreaCode> extends 3
        ? StringLength<Exchange> extends 3
          ? StringLength<Number> extends 4
            ? true
            : false
          : false
        : false
      : false
    : Phone extends `(${infer AreaCode}) ${infer Exchange}-${infer Number}`
      ? StringLength<AreaCode> extends 3
        ? StringLength<Exchange> extends 3
          ? StringLength<Number> extends 4
            ? true
            : false
          : false
        : false
      : false;

// 🔐 Password strength validation
type IsStrongPassword<Password extends string> = 
  StringLength<Password> extends infer Length
    ? Length extends number
      ? Length extends 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20
        ? Contains<Password, "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"> extends true
          ? Contains<Password, "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"> extends true
            ? Contains<Password, "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"> extends true
              ? Contains<Password, "!" | "@" | "#" | "$" | "%" | "^" | "&" | "*"> extends true
                ? true
                : false
              : false
            : false
          : false
        : false
      : false
    : false;

// ✅ Validation examples
type ValidEmail = IsValidEmail<"[email protected]">; // true
type InvalidEmail = IsValidEmail<"invalid-email">; // false

type ValidPhone = IsValidPhoneUS<"(555) 123-4567">; // true
type InvalidPhone = IsValidPhoneUS<"123-456">; // false

type StrongPass = IsStrongPassword<"MyP@ssw0rd123">; // true
type WeakPass = IsStrongPassword<"password">; // false

// 🎯 Credit card validation (Luhn algorithm concept)
type ValidateCreditCard<CardNumber extends string> = 
  // Simplified validation - checks basic format
  CardNumber extends `${infer First4}${infer Second4}${infer Third4}${infer Fourth4}`
    ? StringLength<First4> extends 4
      ? StringLength<Second4> extends 4
        ? StringLength<Third4> extends 4
          ? StringLength<Fourth4> extends 4
            ? true
            : false
          : false
        : false
      : false
    : false;

type ValidCard = ValidateCreditCard<"1234567890123456">; // true
type InvalidCard = ValidateCreditCard<"123456789">; // false

🎨 Advanced String Formatting

// 💰 Currency formatting
type FormatCurrency<
  Amount extends string,
  Currency extends string = "USD",
  Symbol extends string = "$"> = `${Symbol}${Amount} ${Currency}`;

type FormattedPrice = FormatCurrency<"99.99", "USD", "$">; // "$99.99 USD"

// 📅 Date formatting
type FormatDate<
  Year extends string,
  Month extends string,
  Day extends string,
  Format extends "ISO" | "US" | "EU" = "ISO"> = Format extends "ISO"
  ? `${Year}-${Month}-${Day}`
  : Format extends "US"
    ? `${Month}/${Day}/${Year}`
    : Format extends "EU"
      ? `${Day}.${Month}.${Year}`
      : never;

type ISODate = FormatDate<"2024", "06", "20", "ISO">; // "2024-06-20"
type USDate = FormatDate<"2024", "06", "20", "US">; // "06/20/2024"
type EUDate = FormatDate<"2024", "06", "20", "EU">; // "20.06.2024"

// 📊 Number formatting
type FormatNumber<
  Number extends string,
  Separators extends { thousands: string; decimal: string } = { thousands: ","; decimal: "." }
> = Number extends `${infer Integer}.${infer Decimal}`
  ? `${Integer}${Separators["decimal"]}${Decimal}`
  : Number;

// 🎯 Text justification
type JustifyText<
  Text extends string,
  Width extends number,
  Alignment extends "left" | "right" | "center" = "left"> = StringLength<Text> extends infer Len
  ? Len extends number
    ? Len extends Width
      ? Text
      : Alignment extends "left"
        ? Text // Would need padding implementation
        : Alignment extends "right"
          ? Text // Would need padding implementation
          : Text // Would need padding implementation
    : Text
  : Text;

// 📝 Slug generation
type GenerateSlug<Title extends string> = 
  ToLowerCase<
    ReplaceAll<
      ReplaceAll<
        ReplaceAll<Trim<Title>, " ", "-">,
        "_", "-">,
      "--", "-">
  >;

type SlugExample = GenerateSlug<"Hello World Example Title">; // "hello-world-example-title"

// 🏷️ Tag formatting
type FormatHashtags<Text extends string> = 
  Text extends `${infer Before} #${infer Tag} ${infer After}`
    ? `${Before} <span class="hashtag">#${Tag}</span> ${FormatHashtags<After>}`
    : Text extends `${infer Before} #${infer Tag}`
      ? `${Before} <span class="hashtag">#${Tag}</span>`
      : Text;

type HashtagText = FormatHashtags<"Love #TypeScript and #JavaScript">; 
// "Love <span class=\"hashtag\">#TypeScript</span> and <span class=\"hashtag\">#JavaScript</span>"

🧪 Real-World String Processing Applications

🌐 SQL Query Builder

// 🗄️ SQL query construction
type SQLSelect<
  Columns extends string[],
  Table extends string,
  Where extends string = "",
  OrderBy extends string = ""> = `SELECT ${Columns extends readonly [infer First, ...infer Rest]
  ? First extends string
    ? Rest extends string[]
      ? Rest['length'] extends 0
        ? First
        : `${First}, ${SQLSelect<Rest, Table, Where, OrderBy>}`
      : First
    : ""
  : "*"} FROM ${Table}${Where extends "" ? "" : ` WHERE ${Where}`}${OrderBy extends "" ? "" : ` ORDER BY ${OrderBy}`}`;

type UserQuery = SQLSelect<["id", "name", "email"], "users", "active = 1", "created_at DESC">;
// "SELECT id, name, email FROM users WHERE active = 1 ORDER BY created_at DESC"

// 🔍 Safe SQL parameter substitution
type SafeSQLValue<Value extends string | number | boolean> = 
  Value extends string ? `'${Value}'` :
  Value extends number ? `${Value}` :
  Value extends boolean ? Value extends true ? "1" : "0" :
  never;

type SQLWhere<Conditions extends Record<string, string | number | boolean>> = {
  [K in keyof Conditions]: `${K & string} = ${SafeSQLValue<Conditions[K]>}`
}[keyof Conditions];

type WhereClause = SQLWhere<{ name: "John"; age: 30; active: true }>; 
// "name = 'John'" | "age = 30" | "active = 1"

📱 API Endpoint Generation

// 🎯 REST API endpoint generation
type RESTEndpoint<
  Resource extends string,
  Action extends "list" | "create" | "read" | "update" | "delete",
  ID extends string = ""> = Action extends "list"
  ? `/api/${Resource}`
  : Action extends "create"
    ? `/api/${Resource}`
    : Action extends "read"
      ? `/api/${Resource}/${ID}`
      : Action extends "update"
        ? `/api/${Resource}/${ID}`
        : Action extends "delete"
          ? `/api/${Resource}/${ID}`
          : never;

type UserEndpoints = {
  list: RESTEndpoint<"users", "list">;           // "/api/users"
  create: RESTEndpoint<"users", "create">;       // "/api/users"
  read: RESTEndpoint<"users", "read", "123">;    // "/api/users/123"
  update: RESTEndpoint<"users", "update", "123">; // "/api/users/123"
  delete: RESTEndpoint<"users", "delete", "123">; // "/api/users/123"
};

// 🔄 GraphQL query generation
type GraphQLQuery<
  Operation extends "query" | "mutation",
  Name extends string,
  Fields extends string[]
> = `${Operation} {
  ${Name} {
    ${Fields extends readonly [infer First, ...infer Rest]
      ? First extends string
        ? Rest extends string[]
          ? Rest['length'] extends 0
            ? First
            : `${First}
    ${GraphQLQuery<Operation, Name, Rest>}`
          : First
        : ""
      : ""}
  }
}`;

// Would need better formatting, but concept is there
type UserGraphQLQuery = GraphQLQuery<"query", "user", ["id", "name", "email"]>;

🎨 CSS and Style Generation

// 🎨 CSS class name generation
type CSSClassName<
  Component extends string,
  Modifier extends string = "",
  State extends string = ""> = `${Component}${Modifier extends "" ? "" : `--${Modifier}`}${State extends "" ? "" : `__${State}`}`;

type ButtonClasses = {
  base: CSSClassName<"button">;                    // "button"
  primary: CSSClassName<"button", "primary">;     // "button--primary"
  loading: CSSClassName<"button", "primary", "loading">; // "button--primary__loading"
};

// 🎯 CSS property generation
type CSSProperty<Property extends string, Value extends string | number> = 
  `${Property}: ${Value}${Value extends number ? "px" : ""};`;

type CSSRule<Selector extends string, Properties extends Record<string, string | number>> = 
  `${Selector} {
  ${keyof Properties extends string 
    ? {
        [K in keyof Properties]: CSSProperty<K & string, Properties[K]>
      }[keyof Properties]
    : ""}
}`;

// 📱 Responsive breakpoint generation
type Breakpoint<Size extends "sm" | "md" | "lg" | "xl"> = 
  Size extends "sm" ? "576px" :
  Size extends "md" ? "768px" :
  Size extends "lg" ? "992px" :
  Size extends "xl" ? "1200px" :
  never;

type MediaQuery<Size extends "sm" | "md" | "lg" | "xl"> = 
  `@media (min-width: ${Breakpoint<Size>})`;

type ResponsiveClass = MediaQuery<"md">; // "@media (min-width: 768px)"

// 🌈 Color manipulation
type HexColor = `#${string}`;
type RGBColor = `rgb(${number}, ${number}, ${number})`;
type HSLColor = `hsl(${number}, ${number}%, ${number}%)`;

type ColorValue = HexColor | RGBColor | HSLColor;

type CSSColorProperty<Color extends ColorValue> = CSSProperty<"color", Color>;

type RedColor = CSSColorProperty<"#ff0000">; // "color: #ff0000;"

📝 Documentation Generation

// 📚 TypeDoc-style documentation
type GenerateDocComment<
  Description extends string,
  Params extends Record<string, string> = {},
  Returns extends string = "void",
  Example extends string = ""> = `/**
 * ${Description}
${keyof Params extends never ? "" : 
  keyof Params extends string 
    ? ` * @param {string} ${keyof Params} ${Params[keyof Params]}`
    : ""
}${Returns extends "void" ? "" : ` * @returns {${Returns}} Return value description`}${Example extends "" ? "" : `
 * @example
 * ${Example}`}
 */`;

type FunctionDoc = GenerateDocComment<
  "Calculates the sum of two numbers",
  { a: "The first number"; b: "The second number" },
  "number",
  "add(2, 3) // returns 5">;

// 🎯 README.md generation
type GenerateREADME<
  Title extends string,
  Description extends string,
  Installation extends string = "npm install",
  Usage extends string = ""> = `# ${Title}

${Description}

## Installation

\`\`\`bash
${Installation}
\`\`\`

${Usage extends "" ? "" : `## Usage

${Usage}`}

## License

MIT
`;

type ProjectREADME = GenerateREADME<
  "My TypeScript Project",
  "A powerful TypeScript library for string manipulation",
  "npm install my-typescript-project",
  "import { processString } from 'my-typescript-project';">;

🧮 Performance Optimization and Edge Cases

⚡ Optimization Techniques

// 🎯 Memoization for string operations
type StringCache = {};

type CachedOperation<
  Key extends string,
  Operation extends string,
  Cache extends Record<string, any> = StringCache> = Key extends keyof Cache 
  ? Cache[Key]
  : Operation;

// 🔄 Tail recursion optimization
type TailRecursiveReverse<
  S extends string,
  Acc extends string = ""> = S extends `${infer First}${infer Rest}`
  ? TailRecursiveReverse<Rest, `${First}${Acc}`>
  : Acc;

type OptimizedReverse = TailRecursiveReverse<"hello">; // "olleh"

// 🎯 Chunked processing for large strings
type ChunkedProcess<
  S extends string,
  ChunkSize extends number = 10,
  Processed extends string = ""> = StringLength<S> extends infer Len
  ? Len extends number
    ? Len extends 0
      ? Processed
      : S extends `${infer Chunk}${infer Rest}`
        ? ChunkedProcess<Rest, ChunkSize, `${Processed}${Chunk}`>
        : Processed
    : Processed
  : Processed;

// 📊 Performance monitoring
type ComplexityAnalysis<Operation extends string> = {
  operation: Operation;
  timeComplexity: "O(n)" | "O(n²)" | "O(log n)" | "O(1)";
  spaceComplexity: "O(n)" | "O(1)";
  recursionDepth: "shallow" | "deep";
};

type ReverseComplexity = ComplexityAnalysis<"reverse"> & {
  timeComplexity: "O(n)";
  spaceComplexity: "O(n)";
  recursionDepth: "deep";
};

🛡️ Edge Case Handling

// 🎯 Empty string handling
type SafeStringOperation<S extends string, Default extends string = ""> = 
  S extends "" ? Default : S;

// 🔄 Unicode and special character handling
type ContainsUnicode<S extends string> = 
  // Simplified check for basic Unicode detection
  S extends `${string}${infer Char}${string}`
    ? Char extends "🚀" | "🎯" | "✨" | "💻" | "📝" | "🔍" | "🛡️" | "⚡" | "🎨" | "🧮"
      ? true
      : false
    : false;

// 📊 Length limitations and safety
type SafeStringLength<S extends string> = 
  StringLength<S> extends infer Len
    ? Len extends number
      ? Len extends 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 
          | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20
          | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30
        ? Len
        : "too_long"
      : "unknown"
    : "unknown";

// 🎯 Type-safe error handling
type StringOperationResult<T> = 
  T extends string 
    ? { success: true; result: T }
    : { success: false; error: string };

type SafeReplace<S extends string, Search extends string, Replace extends string> = 
  S extends string
    ? Search extends ""
      ? StringOperationResult<never> & { success: false; error: "Empty search string" }
      : StringOperationResult<Replace<S, Search, Replace>>
    : StringOperationResult<never> & { success: false; error: "Invalid input" };

// ✅ Edge case examples
type EmptyOperation = SafeStringOperation<"", "default">; // "default"
type UnicodeCheck = ContainsUnicode<"Hello 🚀 World">; // true
type SafeLength = SafeStringLength<"hello">; // 5
type SafeReplaceResult = SafeReplace<"hello", "l", "x">; // { success: true; result: "hexlo" }

🎓 Key Takeaways

You’ve mastered the art of advanced string manipulation at the type level! Here’s what you now command:

  • ✅ Advanced template literal patterns and string manipulation primitives 💪
  • ✅ Complex string algorithms including search, replace, and transformation 🛡️
  • ✅ Template engines and parsers for compile-time text processing 🎯
  • ✅ String validation systems with advanced pattern matching 🐛
  • ✅ Real-world applications in SQL, APIs, CSS, and documentation generation 🚀
  • ✅ Performance optimization and edge case handling techniques ✨
  • ✅ Type-safe string operations with comprehensive error handling 🔄

Remember: Type-level string operations enable you to build incredibly sophisticated text processing systems that run entirely at compile time! 🤝

🤝 Next Steps

Congratulations! 🎉 You’ve become a master of TypeScript’s string manipulation capabilities!

Here’s what to do next:

  1. 💻 Build template engines and DSL parsers using type-level string operations
  2. 🏗️ Create advanced validation libraries with compile-time string checking
  3. 📚 Move on to our next tutorial: Type-Level Boolean Logic - Conditional Operations
  4. 🌟 Implement SQL query builders and API endpoint generators
  5. 🔍 Explore string interpolation and formatting in other type systems
  6. 🎯 Build documentation generators and code analysis tools
  7. 🚀 Push the boundaries of what’s possible with compile-time text processing

Remember: You now possess the power to manipulate text at the deepest level of TypeScript’s type system! Use this knowledge to build amazing developer tools and libraries. 🚀

Happy string manipulation mastering! 🎉🔤✨

Previous Tutorial
🔢 Type-Level Arithmetic: Number Operations
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🔀 Type-Level Boolean Logic: Conditional Operations

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Part 87

🔢 Type-Level Arithmetic: Number Operations

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🔤 Type-Level String Operations: Advanced Manipulations

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Part 89

🔀 Type-Level Boolean Logic: Conditional Operations

💎Advanced • 28 min read
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Tutorial Info

Series Progress
Part 88 of 355 25%
Category
📘 typescript
Difficulty
💎Advanced
Duration
35 min read
Published
June 20, 2025