Enum
An enum is a type or language construct whose values are selected from a finite set of named alternatives, which may carry associated data.
Learn Go with Pocket-Sized Projects
An enumeration is a finite set of named values representing alternatives of the same conceptual kind.
- How it is used
- Represents logging levels and character-feedback states as named alternatives.
- How deep it goes
- Works through named byte types, iota constants, zero-value ordering, and a Stringer method.
- Examples
- Uses three logger levels and three word-game character hints as concrete implementations.
- What you can do after
- Build it from scratch using a named Go type and iota constants, choosing an order that makes the zero value useful.
Read how Learn Go with Pocket-Sized Projects explains enum →
Secure APIs
An enumeration is a type whose permitted values are restricted to a finite, explicitly defined set of named alternatives.
- How it is used
- Restricts API parameters and data received from external or internal services to values the application explicitly supports.
- How deep it goes
- Defines named alternatives and demonstrates validation and attack prevention, but does not detail enumeration internals.
- Examples
- Uses character statuses, product sorting fields, and printed-versus-ebook formats as concrete constrained-value examples.
- What you can do after
- Apply it via OpenAPI schemas or Pydantic models to reject unsupported values before processing or persistence.
Python How-To
Enumeration is the technique of associating each item in a set of related concepts with a distinct named member of a common category.
- How it is used
- Groups related choices into named members for direction inputs, task statuses, and database options.
- How deep it goes
- Works through Enum construction, member lookup, attributes, iteration, and custom string behavior; contrasts regular class attributes with true members.
- Examples
- Uses compass directions, a movement function, sortable task statuses, and CSV-versus-SQLite database choices.
- What you can do after
- Build it from scratch by subclassing Enum, then use members for typed choices, value lookup, iteration, and readable output.
Refactoring to Rust
An enum is a type whose value is exactly one of a fixed set of named variants, with each variant optionally carrying associated data.
- How it is used
- Uses enums to communicate fixed outcomes between functions and to represent success or failure without exceptions.
- How deep it goes
- Works from named variants through payloads and match expressions, then applies the same model to Result and custom error types.
- Examples
- Refactors a FizzBuzz helper from strings to variants, adds a number-carrying variant, and handles negative input with an error enum.
- What you can do after
- Build it from scratch: define variants, return them from a function, match their payloads, and represent failures with Result.
100 Java Mistakes and How to Avoid Them
An enum type is a Java class-like type that defines a fixed set of named constants.
- How it is used
- Models fixed named states and replaces ambiguous null results with explicit outcomes.
- How deep it goes
- Explains initialization ordering, constructor cycles, values() failure, and pre-Java-21 switch desugaring.
- Examples
- Uses mutually referencing Pet and Voice constants, a DayOfWeek weekend field, user answers, and RoundingMode.UNNECESSARY.
- What you can do after
- Diagnose/debug enum initialization nulls and model distinct absent-result meanings as named constants.
Read how 100 Java Mistakes and How to Avoid Them explains enum →
Rust in Action: Systems programming concepts and techniques
An enum is a type whose value is one of a finite set of named variants, optionally carrying associated data.
- How it is used
- Models fixed choices in event logs, file states, network states, error types, and VGA colors.
- How deep it goes
- Works through enum syntax, data-carrying variants, matching, state checks, and error conversion; defers advanced state-machine methods.
- Examples
- Uses card suits, parsed event logs, mock files, wrapped errors, network states, and VGA colors.
- What you can do after
- Build it from scratch to represent named alternatives, carry variant-specific data, and check file state before reading.
Read how Rust in Action: Systems programming concepts and techniques explains enum →
Learn Rust in a Month of Lunches
An enum is a Rust user-defined type whose values are one of a fixed set of named variants, optionally carrying associated data.
- How it is used
- Represents one choice among named variants, including choices stored in structs or used to hold different payload types in one collection.
- How deep it goes
- Works through declaration, matching, associated data, integer casting, and methods using small examples.
- Examples
- Uses climate choices, sun-or-stars states, signed and unsigned numbers in a Vec, and a mood-checking method.
- What you can do after
- Build it from scratch: declare variants, attach data, match on choices, and store different payloads under one enum type.
Essential TypeScript 5, Third Edition
An enum value is a named value belonging to an enum.
- How it is used
- Names related values for consistent use in product processing and interactive application commands.
- How deep it goes
- Explains declaration, numeric and string values, generated JavaScript, const enums, and value-checking limitations.
- Examples
- Demonstrates product prices in tuples and command selection in a to-do application using Inquirer.js.
- What you can do after
- Build it from scratch with named numeric or string members, then use those members in application decisions.
Read how Essential TypeScript 5, Third Edition explains enum →
Software Design for Python Programmers
An enumeration type defines a fixed set of named constant values.
- How it is used
- Constrains book genres to a fixed set while reducing typo and comparison risks in catalogue searches.
- How deep it goes
- Defines enumeration constants and contrasts them with strings, but does not explore enumeration internals.
- Examples
- Uses book genres such as ADVENTURE and CLASSICS in Python catalogue construction and search examples.
- What you can do after
- Apply it via Python's Enum class to represent a bounded attribute safely.
Read how Software Design for Python Programmers explains enum →
Functional Programming in Scala, Second Edition
An enumeration is a type declaration that defines a finite set of named data constructors.
- How it is used
- Defines algebraic data types by enumerating their permitted data constructors.
- How deep it goes
- Explains constructors, type parameters, recursive cases, pattern matching, and sealed-trait alternatives, but defers incidental syntax details.
- Examples
- Uses singly linked lists with Nil and Cons, plus trees with Leaf and Branch, as recursive enum examples.
- What you can do after
- Build algebraic data types and process their cases with recursive, pattern-matching functions.
Read how Functional Programming in Scala, Second Edition explains enum →
The Design of Web APIs, Second Edition
An enumerated status string is a textual value constrained to one item from a predefined set of status values.
- How it is used
- Constrains API values to controlled alternatives for clearer data, flexible filtering, and interoperable consumer contracts.
- How deep it goes
- Explains readable values, legacy labels, filtering syntax, JSON Schema precision, and compatibility effects without covering implementation internals.
- Examples
- Uses bank-account types, transaction categories, recurring periods, transfer currencies, and categorization statuses as concrete cases.
- What you can do after
- Evaluate enumeration choices and apply them to API values, filters, schemas, and compatibility decisions.
Read how The Design of Web APIs, Second Edition explains enum →
DuckDB in Action
An enum is a data type whose values are restricted to a defined set of named alternatives.
- How it is used
- Uses fixed-value enums to optimize analytical storage, processing, and filtering of large categorical datasets.
- How deep it goes
- Explains integer storage, creation, conversion, functions, and query comparisons, but does not detail execution internals.
- Examples
- Demonstrates weekday values, tag vocabularies, enum lists, membership filters, and top-tag aggregation queries.
- What you can do after
- Apply it via DuckDB SQL to model categorical values, convert string columns, and query large tag datasets efficiently.
Build Financial Software with Generative AI (From Scratch)
An enum type is a database type whose permitted values are defined by a finite named set of labels.
- How it is used
- Uses finite labels to enforce consistent categories in ACH exceptions and company information schemas.
- How deep it goes
- Explains declaration, column usage, label extraction, tradeoffs, and a lookup-table alternative, but not enum internals.
- Examples
- Demonstrates exception severities, tax identifier types, industries, address types, and phone categories.
- What you can do after
- Build it from scratch in PostgreSQL and evaluate whether a lookup table better fits portability or changing values.
Read how Build Financial Software with Generative AI (From Scratch) explains enum →
Learn Haskell by Example
An enumeration type is an algebraic data type whose constructors are all nullary and whose values form a finite enumerable set.
- How it is used
- Enumerates nullary constructors for ranges, ordering-based traversal, and numeric conversion.
- How deep it goes
- Defines Enum methods and derived behavior, but stops short of implementation internals.
- Examples
- Uses EnumType with A, B, and C plus FileType with Other, Image, and Compressed.
- What you can do after
- Apply it via derived Enum and Bounded instances to build complete constructor lists and numeric mappings.
Building User-Friendly DSLs
An enumeration is a language construct that defines a fixed collection of permitted named values.
- How it is used
- Defines fixed textual choices within an MPS DSL’s structure aspect.
- How deep it goes
- Defines the construct and gives one concrete value set, but does not detail declaration or code-generation mechanics.
- Examples
- Uses the Type enumeration with amount, date range, and percentage values.
- What you can do after
- Evaluate fixed DSL value categories using a concrete enumeration definition.
Kotlin in Action, 2E
An enum is a Kotlin type whose instances are restricted to a fixed set of named constants.
- How it is used
- Represents fixed choices and dispatches behavior through when expressions.
- How deep it goes
- Explains declarations, constructor data, properties, methods, grouped matching, and imports, but stops short of advanced enum mechanics.
- Examples
- Uses Color constants, RGB values, a color-printing method, a mnemonic function, and sensor-based warmth categories.
- What you can do after
- Apply it by declaring Kotlin enums with data and selecting exhaustive behavior through when.
The Art of Code
An enum is a language construct that defines a finite set of named constants as a distinct type.
- How it is used
- Represents fixed, known categories explicitly so data constraints and intent remain visible.
- How deep it goes
- Explains the modeling rationale and tradeoff with strings or numeric codes, but stops short of syntax or runtime behavior.
- Examples
- Contrasts enums with free-form strings and numeric codes for representing closed sets of values.
- What you can do after
- Apply it by modeling fixed categories explicitly and routing limited data-driven variation through clear branching.
Object-Oriented Software Design in C++
A type whose values are restricted to a finite set of named constants.
- How it is used
- Constrains book genres to a finite set of named values while avoiding string comparison and spelling problems.
- How deep it goes
- Defines an enum class, demonstrates its constants, and stops short of broader enumeration design concerns.
- Examples
- Uses book genres including ADVENTURE, CLASSICS, HORROR, and SCIFI in construction and catalogue-search examples.
- What you can do after
- Evaluate whether a limited attribute should use an enumeration rather than a string.
Read how Object-Oriented Software Design in C++ explains enum →
Code Like a Pro in Rust
An enum is a Rust type that represents a value selected from a defined set of variants, which may carry associated data.
- How it is used
- Models mutually exclusive states, named choices, and choices carrying variant-specific data.
- How deep it goes
- Defines variant forms, discriminant casts, and manual numeric conversion, but does not develop broader enum control-flow patterns.
- Examples
- Uses Japanese dog breeds, explicit numeric variants, Debug output, From<u32>, and mixed named, tuple, and struct-like variants.
- What you can do after
- Build it from scratch as a Rust enum, attach heterogeneous variant data, derive traits, cast discriminants, and implement numeric conversion.
Write Powerful Rust Macros
An enum is a Rust sum type with a fixed set of named variants that may carry associated data and methods.
- How it is used
- Models restricted states and makes success-or-failure outcomes explicit in error handling.
- How deep it goes
- Explains variants, associated data, pattern matching, generics, and a convenience method without descending into representation internals.
- Examples
- Uses an `Either<T>` result, a calculation returning `Success(42)`, exhaustive matching, and a `map` transformation.
- What you can do after
- Apply enums to represent recoverable outcomes and handle each variant through pattern matching.
Modern C, Third Edition
An enumeration is a C type that defines a set of named integer values.
- How it is used
- Names small integer values and stabilizes array indexing without manually tracking entry order.
- How deep it goes
- Explains positional and explicit values, conversions, and integer constant expressions, but does not develop enumeration storage mechanics.
- Examples
- Uses corvid names, a designated string array, sequential constants, and valid or invalid constant-expression definitions.
- What you can do after
- Apply it via named constants and designated array indices while respecting compile-time value constraints.
Practical Automation with PowerShell: Effective scripting from the console to the cloud
An enumeration is a set of named constants, typically associated with underlying integral values.
- How it is used
- Uses named constants to supply readable options when PowerShell calls APIs such as Microsoft Word automation.
- How deep it goes
- Explains integer backing values, qualified syntax, value discovery, and API usage, while deferring custom enumeration design.
- Examples
- Demonstrates Word table auto-fit modes, GetEnumValues output, table creation, and constrained server-status parameters.
- What you can do after
- Apply it via PowerShell to select documented API behaviors and inspect valid enum values without relying on numeric codes.
100 C++ Mistakes and How to Avoid Them
An enumeration is a C++ type that defines a set of named integral values representing a finite collection of alternatives.
- How it is used
- Uses named alternatives to make values such as colors readable in automobile and traffic-light code.
- How deep it goes
- Explains global-name collisions, integer ambiguity, default values, and scoped corrections through contrasting code listings.
- Examples
- Uses traffic-light colors, automobile paint colors, integer color values, and separate Traffic and Paint enums.
- What you can do after
- Apply it via enum class to separate related value sets and write qualified switch cases.
Read how 100 C++ Mistakes and How to Avoid Them explains enum →
Related concepts
- result typeincludes · A type that represents an operation’s outcome as either a successful value or a failure value.
- sealed traitalternative to · A sealed trait is a Scala trait whose permitted subtypes are restricted to declarations known to the compiler.
- data structurekind of · A data structure is an organized representation of data and its relationships that supports defined operations for storing, accessing, or modifying it.
- enum varianthas part · An enum variant is one named alternative in an enumeration’s finite set of possible values, optionally containing associated data.
- booleanalternative to · A Boolean is a logical type or value representing truth or falsity, conventionally with two states: true and false.
- enum constanthas part · An enumeration constant is a named member of an enumeration representing one distinct enumerated value.
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