Symbol
A symbol is a name or sign that represents or identifies a value, entity, operation, or concept within a notation or system.
The Joy of JavaScript
Symbol is the JavaScript built-in function object used to create symbol values, with static methods for symbol-related operations such as global lookup.
- How it is used
- Uses symbols as collision-free property keys and shared behavioral contracts for objects across application components.
- How deep it goes
- Explains creation, identity, property access, reflection, and global-registry lookup, then applies those mechanics to application contracts.
- Examples
- Shows duplicate descriptions yielding distinct symbols, a version-keyed mining workflow, and a symbol-keyed JSON serialization hook.
- What you can do after
- Apply it via `Symbol`, `Symbol.for`, and `Symbol.keyFor` to define collision-free keys and shared application hooks.
The Well-Grounded Rubyist, Fourth Edition
Symbol is Ruby's built-in class whose instances are immutable symbol values representing distinct names or identifiers.
- How it is used
- Serves as an immutable name value for method arguments and hash keys.
- How deep it goes
- Explains literals, conversion, identity, immutability, and the symbol table, but does not develop hash behavior in depth.
- Examples
- Compares object IDs for string and symbol literals, then uses `send`, `attr_reader`, and symbol-keyed hashes.
- What you can do after
- Apply it via Ruby symbol literals and conversions when passing method names or choosing hash keys.
Read how The Well-Grounded Rubyist, Fourth Edition explains symbol →
Get Programming with JavaScript Next: New features of ECMAScript 2015, 2016, and beyond
A symbol value that is guaranteed not to be equal to any other symbol value.
- How it is used
- Uses symbols to prevent flag collisions, name less-visible object properties, and hook into object behavior.
- How deep it goes
- Works through identity, property visibility, coercion hooks, and errors, while deferring most well-known symbols.
- Examples
- Uses tooltip flags, coercion with Symbol.toPrimitive, and a lock-and-key exercise.
- What you can do after
- Build it from scratch: create collision-free flags or a lock whose key matches only its original symbol.
Clojure: The Essential Reference
A Clojure symbol is a symbolic identifier that can name a var, local binding, or function parameter, appear as code data, carry metadata, and optionally include a namespace qualification.
- How it is used
- Names vars, local bindings, and function parameters while distinguishing program identifiers from data and ordinary text.
- How deep it goes
- Explains lookup, metadata, qualification, construction, and reader validation, but does not develop symbol internals beyond their Clojure class.
- Examples
- Uses symbol construction, namespace extraction, equality checks, read-string, and macro expansion to expose symbol behavior.
- What you can do after
- Evaluate/understand how Clojure represents identifiers, resolves them, qualifies them, and preserves them in code data.
Julia as a Second Language
A symbol is a Julia identifier form that can name a function and, when suitable, enable infix invocation.
- How it is used
- Uses symbols to name functions, enable infix invocation, and represent programmer-facing option labels.
- How deep it goes
- Defines symbols through runnable calls and a custom operator, then demonstrates symbol construction; it does not develop deeper implementation details.
- Examples
- Demonstrates +, -, a custom × function, printstyled color :cyan, and Symbol("hello") compared with :hello.
- What you can do after
- Apply it via Julia syntax to call symbolic functions in prefix or infix form and supply symbolic labels to printstyled.
Related concepts
- let keywordused by · A let construct is a language feature that introduces a name binding associating an identifier with a value or expression.
- methodsproduced by · A language-level introspection facility that reports methods associated with an object or function.
- methodproduced by · A method is a callable operation associated with an object or type and invoked through that association.
- to_symproduced by · to_sym is a Ruby conversion method that returns a symbol corresponding to a value's textual representation.
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