Type constraint
A type constraint is a rule that restricts admissible types or type arguments by requiring specified relationships, structures, properties, or supported operations.
Go in Action, Second Edition
A type constraint restricts the types that may be substituted for a type parameter and specifies operations guaranteed to be valid for those types.
- How it is used
- Restricts generic functions and collections to compatible types while making required operations explicit.
- How deep it goes
- Works through built-in constraints, custom type sets, underlying-type matching, multiple parameters, compiler errors, and performance considerations.
- Examples
- Uses recipe filtering, numeric addition, linked lists, and a map with separately constrained keys and values.
- What you can do after
- Build it from scratch: choose constraints for type-safe Go functions and collections, then check operator requirements and benchmark when needed.
Read how Go in Action, Second Edition explains type constraint →
Learn Go with Pocket-Sized Projects
A type constraint is an interface-based restriction specifying which types may be used as a generic type argument.
- How it is used
- Constrains generic functions, structures, and variables so reusable declarations accept types with the required capabilities.
- How deep it goes
- Explains any, comparable, Ordered, unions, and underlying-type matching with ~ through focused declarations and examples.
- Examples
- Uses prettyPrint, fmt.Stringer, summable integer unions, defined age types, and an Ordered sortSlice function.
- What you can do after
- Build generic declarations that restrict accepted types and enable operations such as equality, ordering, or formatted output.
Read how Learn Go with Pocket-Sized Projects explains type constraint →
Essential TypeScript 5, Third Edition
A generic type constraint restricts the types that may be supplied for a generic type parameter by requiring them to satisfy a specified type relationship or shape.
- How it is used
- Restricts generic type arguments so collections and decorators can rely on required properties, signatures, or value types.
- How deep it goes
- Works through union and shape constraints, then applies constructor, method-result, and field constraints; does not pursue advanced generic features.
- Examples
- Uses named collections of people, products, and cities, plus method, class, and numeric-field decorators.
- What you can do after
- Build it from scratch: constrain a generic collection or decorator to the types its implementation can handle.
Read how Essential TypeScript 5, Third Edition explains type constraint →
Go in Practice, Second Edition
A type constraint is a generic declaration that restricts a type parameter to a specified set of types.
- How it is used
- Constrains generic functions when reusable code must accept a deliberate subset of types.
- How deep it goes
- Explains unions, exact types, underlying types, tilde approximation, and the experimental constraints package through runnable examples.
- Examples
- Uses Animal unions, generic slice filters, Numeric filters, named Smallint values, and constraints.Integer.
- What you can do after
- Build generic functions that accept precise type sets and support named underlying types when constraints use approximation.
Read how Go in Practice, Second Edition explains type constraint →
Learn Haskell by Example
Constraint is the Haskell kind-level type representing a type-class constraint.
- How it is used
- Constrains polymorphic functions so their implementations may safely use operations supplied by a type class.
- How deep it goes
- Defines constraints through Eq signatures and kind-level Constraint, but does not descend into compiler implementation internals.
- Examples
- Uses equality-based associative-list membership and GHCi inspections of Eq, Functor, and type and kind signatures.
- What you can do after
- Diagnose type errors, write accurate polymorphic signatures, and inspect unfamiliar constraints with GHCi.
Read how Learn Haskell by Example explains type constraint →
100 Go Mistakes and How to Avoid Them
A constraint is a Go interface type that restricts the types permitted as generic type arguments.
- How it is used
- Restricts generic type arguments so functions such as getKeys accept only keys meeting required operations or type sets.
- How deep it goes
- Explains comparable keys, custom unions, underlying-type approximation, and method intersections, stopping before broader generic design.
- Examples
- Uses generic getKeys, invalid slice map keys, customConstraint, explicit type arguments, and a customInt String method.
- What you can do after
- Build it from scratch by defining constraints that prevent invalid generic calls and express permitted type sets.
Read how 100 Go Mistakes and How to Avoid Them explains type constraint →
Related concepts
- inheritanceconfigured by · Inheritance is a mechanism by which a child type or element receives properties, values, or behavior from a parent, subject to system rules and possible overrides.
- atomic typeconfigures · An atomic type is a type whose supported accesses and operations are indivisible with respect to concurrent execution and provide defined synchronization semantics.
- empty interfaceincludes · any is a type or type constraint that permits values of arbitrary concrete types without requiring a more specific interface or representation.
- comparableincludes · comparable is Go’s predeclared generic constraint satisfied by types whose values can be compared with == or !=.
- type argumentconfigures · A type argument is an argument supplied to a parameterized construct to specify a type or constrain the kinds of values it accepts.
These guides are generated from the text of Manning books by Manning's knowledge graph and link to the sections they draw on. The full books are available on liveBook and at manning.com.