Smart constructor
A smart constructor is a constructor-like function that creates values while enforcing constraints or hiding their concrete representation.
Functional Design and Architecture: Examples in Haskell
A smart constructor is a specialized construction function that creates values while presenting a more convenient or constrained interface than the underlying data constructor.
- How it is used
- Defines stable construction interfaces for abstract domain values, service fields, and embedded-language operations.
- How deep it goes
- Explains wrappers, opaque exports, invariant enforcement, serialization, error conversion, and Free/Pure wrapping, while deferring native exception mechanics.
- Examples
- Uses Value wrappers, sensor/controller definitions, sandwich scripts, Sentry timestamp fields, and filesystem writes.
- What you can do after
- Apply it by exposing construction functions that preserve selected invariants and hide representation or integration details.
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Functional Programming in Scala, Second Edition
A smart constructor is a constructor-like function that creates a value while returning an abstraction's base type rather than a concrete data-constructor type.
- How it is used
- Uses constructor-like functions to preserve invariants, control evaluation, and hide repetitive thunk or memoization mechanics.
- How deep it goes
- Works through by-name parameters, lazy vals, cached forcing, and base-type inference, but defers broader lazy construction techniques.
- Examples
- Demonstrates memoized cons, empty, and LazyList.apply construction, alongside direct Cons construction that recomputes an expensive expression.
- What you can do after
- Build it from scratch by defining constructors that defer evaluation, memoize results, enforce invariants, or return abstraction-level types.
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Learn Haskell by Example
A smart constructor is a constructor-like function that creates values while enforcing validity conditions or representation invariants.
- How it is used
- Uses checked construction to create CSV values whose structural invariants remain satisfied.
- How deep it goes
- Explains invariant checks, Either-based errors, safe construction, and an unsafe exception-producing alternative.
- Examples
- Uses CSV headers, columns, equal-length checks, mkCsv results, and unsafeMkCsv exceptions.
- What you can do after
- Build it from scratch by returning Either for invalid inputs and reserving crashing constructors for already-validated data.
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Related concepts
- memoizationimplements · Memoization is an optimization technique that stores computation results with their inputs so equivalent later evaluations can reuse them without recomputation.
- factoryequivalent to · A factory is a function, method, class, or component that creates and returns objects or other values while encapsulating construction details or selection.
- invariantaddresses · An invariant is a property or condition that remains true across the valid states, operations, or specified transformations of a system or computation.
- type systemcontrasts with · A type system is a programming language’s set of rules and mechanisms for classifying values and expressions and constraining their valid uses and combinations.
- algebraic data typeuses · An algebraic data type is a composite type whose values are formed from product structures, finite alternatives, or both through type constructors.
- generalized algebraic data typeused by · A generalized algebraic data type is an algebraic data type whose constructors can impose more specific types on its type parameters.
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