Constant
A constant is a named program value or binding that is fixed or intended not to change after initialization.
The Well-Grounded Rubyist, Fourth Edition
A constant is a Ruby identifier whose name begins with an uppercase letter and conventionally denotes a value intended not to be reassigned.
- How it is used
- Names classes and stores shared class data while making nested values reachable through class or module paths.
- How deep it goes
- Works through assignment, reassignment warnings, object mutation, and relative versus absolute lookup.
- Examples
- Uses a class’s venue array, Math::PI, and nested X definitions to illustrate storage and lookup.
- What you can do after
- Evaluate/understand Ruby constant lookup and distinguish reassignment warnings from changes to referenced objects.
Read how The Well-Grounded Rubyist, Fourth Edition explains constant →
Modern C
A named constant is a constant associated with an explanatory name representing a particular meaning.
- How it is used
- Uses names to preserve distinct meanings, improve maintenance, and identify constants as significant artifacts.
- How deep it goes
- Defines naming principles and surveys enumeration constants, macros, and temporary objects without detailing their syntax.
- Examples
- Uses repeated 3 values, named string arrays, and identifiers such as corvid_num, M_PI, false, true, SIZE_MAX, and fortytwo.
- What you can do after
- Evaluate which repeated values require names and distinguish enumeration constants, macros, and temporary objects by role.
Modern C, Third Edition
A named constant is a program constant given an identifier so code can refer to its meaning instead of repeating its value.
- How it is used
- Uses named constants to express meaning, prevent repeated special values, and improve maintenance and portability.
- How deep it goes
- Distinguishes enumeration constants, macros, compound literals, and C23 constexpr objects but defers their detailed mechanics.
- Examples
- Uses repeated array size 3, corvid_num, M_PI, false, true, SIZE_MAX, and fortytwo as naming examples.
- What you can do after
- Apply semantic naming to replace repeated values and select among C mechanisms for named or compile-time constants.
Related concepts
- inputincludes · An input is a value, information, or signal supplied to a system, computation, or interface for processing or to influence its behavior.
- const qualifierused by · A language feature that marks a value, binding, or access path as constant, restricting reassignment or modification according to the language’s rules.
- enum constantincludes · An enumeration constant is a named member of an enumeration representing one distinct enumerated value.
- double-colon constant lookup tokenused by · The double-colon constant lookup token is Ruby's :: syntax for qualifying and resolving a constant through a class or module hierarchy.
- static fieldcontrasts with · A named variable whose storage is associated with a class or has static duration, rather than being allocated separately for each object instance or function call.
- genericscontrasts with · Generics are programming-language constructs that parameterize or generalize types and operations so they can apply to multiple concrete types or input forms.
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