Types

KaType is a fundamental concept in the Analysis API, representing types of Kotlin expressions and declarations. It provides information about the type structure, nullability, and annotations.

KaType Hierarchy

The KaType interface serves as the base for specific type kinds:

KaClassType: Represents types of classes, objects, and interfaces. This includes both named class types (e.g., String, Int) and types of anonymous objects. For function types like (Int) -> String, there is a KaFunctionType subtype.
KaTypeParameterType: Represents type parameter types, such as T in class Box<T>().
KaCapturedType: Represents captured types.
KaDefinitelyNotNullType: Represents a T & Any type.
KaFlexibleType: Represents types with both a lower and upper bound, such as String? or (Mutable)List<Int>.
KaIntersectionType: Represents types that are intersections of other types.
KaDynamicType: Represents dynamic types, used for interoperability with dynamically typed languages (e.g., JavaScript).
KaErrorType: Represents unresolved types, providing information about the error.

Example

The following example demonstrates how to obtain the KaType of a KtExpression and render its type:

val expression: KtExpression = ...

analyze(expression) {
    val type = expression.expressionType
    if (type is KaClassType) {
        // Analyze the class type
        val className = type.classId.asSingleFqName().asString()
        println(className)
    }
}

Avoid using FqNames or raw strings for type comparison. Use ClassIds instead:

val MY_CLASS_ID = ClassId.fromString("my/app/MyClass")

fun check(expression: KtExpression): Boolean {
    analyze(expression) {
        val type = expression.expressionType
        return type is KaClassType && type.isClassType(MY_CLASS_ID)
    }
}

Getting a `KaType`

You have already seen how to get the expression type. Here is the complete list of utilities that convert either PSI or symbols to types:

val KtTypeReference.type: KaType

A resolved reference type.

val KtExpression.expressionType: KaType?

The expression type, or null if the given expression does not contribute a value.

Particularly, the method returns:

A not-null type for valued expressions (e.g., a variable, a function call, a lambda expression);
Unit for statements (e.g., assignments, loops);
null for KtExpressions that are not a part of the expression tree (e.g., expressions in import or package statements).

val PsiElement.expectedType: KaType?

The expected type for the given element, or null if the element does not have an expected type.

The expected type is the type that the expression is expected to have in the context where it appears.

val KtDeclarationWithReturnType.returnType: KaType

The return type of the given KtDeclarationWithReturnType.

Note: For vararg foo: T parameter returns full Array<out T> type (unlike KaValueParameterSymbol.returnType, which returns T).

val KtFunction.functionType: KaType

The functional type of the given KtFunction.

Depending on the function's attributes, such as suspend or reflective access, different functional type, such as SuspendFunction, KFunction, or KSuspendFunction, will be constructed.

val KaNamedClassSymbol.defaultType: KaType

A class type where type parameters are substituted with matching type parameter types, e.g. List<T> for the List class.

val KtDoubleColonExpression.receiverType: KaType?

Receiver type of the foo::bar expression, or null if the expression is unresolved, or if the resolved callable reference is not of a reflection type.

Comparing `KaType`s

Equivalence check

To check if two types are equivalent, use semanticallyEquals():

val type1: KaType = ...
val type2: KaType = ...

val areEqual = type1.semanticallyEquals(type2)

Comparing to type1 == type2, which only considers simple structural equivalence, semanticallyEquals() ensures that type1 can be substituted with type2.

Subtyping check

To determine if one type is a subtype of another, use isSubtypeOf:

val subtype: KaType = ...
val supertype: KaType = ...

val isSubtype = subtype.isSubtypeOf(supertype)

Building `KaType`s

The Analysis API provides facilities for constructing KaType instances, representing various Kotlin types. The entry point for the type building DSL is typeCreator accessible directly inside the analyze block.

Here's how you can build different types:

Building Class Types

To build a KaClassType, use the typeCreator.classType function. You can specify the target class either by its ClassId or using a KaClassLikeSymbol:

By a class ID:

analyze(ktFile) {
    val intType = typeCreator.classType(KaStandardTypeClassIds.INT)
}

By a class symbol:

analyze(ktFile) {
    val listSymbol: KaClassLikeSymbol = ...
    val listOfStringType = typeCreator.classType(listSymbol) {
        invariantTypeArgument(builtinTypes.string)
    }
}

Specifying Type Arguments:

Within the classType block, you can specify type arguments using the typeArgument function. This function accepts either a KaTypeProjection or a KaType and optionally its variance:

analyze(ktFile) {
    val mapType = typeCreator.classType(KaStandardTypeClassIds.MAP) { 
        typeArgument(Variance.IN_VARIANCE) { 
            builtinTypes.int
        }
        typeArgument(Variance.OUT_VARIANCE, builtinTypes.string)
    }
}

There is also invariantTypeArgument that allows adding a type argument with Variance.INVARIANT. If the type expects more type arguments than provided, the remaining ones are filled with KaStarTypeProjection (*). Excessive type arguments are discarded.

Nullability:

You can also set the nullability of the constructed type by modifying the isMarkedNullable property within the builder:

analyze(ktFile) {
    val nullableStringType = typeCreator.classType(KaStandardTypeClassIds.STRING) {
        isMarkedNullable = true
    }
}

Building Array Types

If you'd like to build an array type, you can still use typeCreator.classType with the desired array ClassId. However, there is a more safe and convenient way to do it using typeCreator.arrayType:

analyze(ktFile) {
    val elementType: KaType = builtinTypes.int
    val nullableIntArrayWithOutVariance = typeCreator.arrayType(elementType) { 
        variance = Variance.OUT_VARIANCE
        isMarkedNullable = true
    }
}

By default, the builder constructs primitive array types when possible. E.g., for the Int element type, IntArray is constructed instead of Array<Int>. You can override this behavior by setting the shouldPreferPrimitiveTypes property within the builder to false.

Note: There is also a shortcut for constructing vararg array types, i.e., the underlying type of vararg function parameters with the given type. You can use typeCreator.varargArrayType for that:

analyze(ktFile) {
    val elementType: KaType = builtinTypes.string
    val stringBoxedArrayType = typeCreator.varargArrayType(elementType)
}

Building Function Types

KaFunctionType can be constructed with typeCreator.functionType:

analyze(ktFile) { 
    val reflectFuctionType = typeCreator.functionType { 
        isReflectType = true
        valueParameter(Name.identifier("first")) {
            builtinTypes.int
        }
        returnType = builtinTypes.string 
    }
}

Specifying Return Type

The return type is defined by returnType. By default, it's set to Unit.

analyze(ktFile) { 
    val functionReturningAny = typeCreator.functionType {
        returnType = builtinTypes.any 
    }

    val functionReturningUnit = typeCreator.functionType()
}

Specifying Parameters

The receiver type parameter can be set using receiverType. By default, it's set to null which indicates that the function is not an extension one.

analyze(ktFile) { 
    val extensionFunctionOnInt = typeCreator.functionType { 
        receiverType = builtinTypes.int
    }
}

Value parameters can be constructed using valueParameter. The API accepts an optional name and a type for the produced parameter:

analyze(ktFile) { 
    val myFunction = typeCreator.functionType { 
        valueParameter(Name.identifier("first")) {
            classType(...) {
                ...
            }
        }
        valueParameter(null, builtinTypes.nullableAny)
    }
}

The builder supports experimental context parameters as well. They can be added via contextParameter which accepts just a type:

analyze(ktFile) { 
    val myFunctionWithContextParameters = typeCreator.functionType {
        contextParameter {
            classType(...) {
                ...
            }
        }
        contextParameter(builtinTypes.int)
    }
}

Note: Kotlin prohibits context parameters in reflection types. All context parameters passed to the builder are discarded when isReflectType is set to true.

Creating Suspending and Reflection Function Types

typeCreator.functionType allows specifying whether the produces KaFunctionType is a suspending function type or a reflection function type. This is controlled by isSuspend and isReflectType respectively, the defaults are set to false.

analyze(ktFile) { 
    val reflectFunctionType = typeCreator.functionType { 
        isReflectType = true
    }

    val suspendingFunctionType = typeCreator.functionType { 
        isSuspend = true
    }
}

Note: Kotlin prohibits context parameters in reflection types. All context parameters passed to the builder are discarded when isReflectType is set to true.

Building Type Parameter Types

To build a KaTypeParameterType, use the typeCreator.typeParameterType function. You need to provide the corresponding KaTypeParameterSymbol:

analyze(ktFile) {
    val typeParameterSymbol: KaTypeParameterSymbol = ...
    val type = typeCreator.typeParameterType(typeParameterSymbol)
}

Note: Similar to class types, you can adjust the nullability of the type parameter type by using isMarkedNullable within the builder.

Building Definitely Not Null Types

KaDefinitelyNotNullType can be constructed using typeCreator.definitelyNotNullType by providing either a KaCapturedType or a KaTypeParameterType.

Note: If the original type was not nullable, typeCreator.definitelyNotNullType returns the original type as no additional wrapping is required.

By a captured type :

analyze(ktFile) {
    val capturedType: KaCapturedType = ...
    val definitelyNotNullParameterType = typeCreator.definitelyNotNullType(capturedType)
}

By a type parameter type:

analyze(ktFile) {
  val typeParameterType: KaTypeParameterType = ...
  val definitelyNotNullParameterType = typeCreator.definitelyNotNullType(typeParameterType)
}

Building Intersection Types

KaIntersectionType can be constructed using typeCreator.intersectionType by building a list of conjuncts via conjunct and conjuncts:

analyze(ktFile) {
  val intersectionType = typeCreator.intersectionType {
    conjunct(builtinTypes.throwable)
    conjuncts(listOf(builtinTypes.int, builtinTypes.any))
    conjunct {
      arrayType(builtinTypes.char)
    }
    conjunct {
      dynamicType()
    }
  }
}

Note: The result of typeCreator.intersectionType is normalized, so it's not always a KaIntersectionType. However, the resulting type is guaranteed to represent a subtype of all the passed conjuncts.

Building Captured Types

KaCapturedType can be constructed using typeCreator.capturedType by providing either a KaTypeProjection or another KaCapturedType:

By a captured type:

analyze(ktFile) {
    val capturedType: KaCapturedType = ...
    val capturedType = typeCreator.capturedType(capturedType) {
        isMarkedNullable = true
    }
}

By a type projection

analyze(ktFile) {
    val typeProjection: KaTypeProjection = ...
    val capturedType = typeCreator.capturedType(typeProjection)
}

Note: If the passed KaTypeProjection is a KaTypeArgumentWithVariance, its variance cannot be Variance.INVARIANT. That's because captured types are intended to capture non-invariant projections. Otherwise, an exception is thrown.

Building Flexible Types

KaFlexibleType can be constructed using typeCreator.flexibleType using three different ways.

If one of the provided bounds is a KaFlexibleType, the corresponding bound of this type is taken instead. E.g., if the upper bound is a flexible type itself, then its upper bound is taken instead.

If the lower bound is not a subtype of the upper bound, null is returned.

If bounds are equal, then it's unnecessary to create a flexible type for them, so this bound type is returned instead.

By another flexible type

analyze(ktFile) {
    val anotherFlexibleType: KaFlexibleType = ...
    val flexibleType = typeCreator.flexibleType(anotherFlexibleType) {
        lowerBound = builtinTypes.int
    }
}

By providing bounds manually

analyze(ktFile) {
    val flexibleType = typeCreator.flexibleType(builtinTypes.int, builtinTypes.any)
}

By providing bounds in the builder

analyze(ktFile) {
    val flexibleType = typeCreator.flexibleType {
        lowerBound = arrayType(builtinTypes.int) {
            shouldPreferPrimitiveTypes = false
            isMarkedNullable = true
        }
        upperBound = builtinTypes.any
    }
}

Building Dynamic Types

KaDynamicType can be constructed using typeCreator.dynamicType:

analyze(ktFile) {
    val dynamicType = typeCreator.dynamicType()
}

Building Annotated Types

Each type except for KaIntersectionType can be constructed with additional annotations. To add annotations to your type, call annotation or annotations with desired annotation ClassIds within the builder.

analyze(ktFile) {
    val myAnnotation: ClassId = ...
    val myAdditionalAnnotations: Iterable<ClassId> = ... 
    val dynamicType = typeCreator.dynamicType {
        annotation(myAnnotation)
        annotations(myAdditionalAnnotations)
    }
}

Note: At the moment, only annotations without value arguments are supported. All annotations requiring arguments are discarded.

Building Type Projections

Building Type Arguments With Variance

KaTypeArgumentWithVariance can be constructed using typeCreator.typeProjection by providing a KaType along with its Variance:

analyze(ktFile) {
    val intTypeWithOutVariance: KaTypeArgumentWithVariance =
        typeCreator.typeProjection(Variance.OUT_VARIANCE, builtinTypes.int)
}

analyze(ktFile) {
    val invariantNullableStringTypeArgument: KaTypeArgumentWithVariance =
        typeCreator.typeProjection(Variance.INVARIANT) {
            classType(KaStandardTypeClassIds.STRING) {
                isMarkedNullable = true
            }
        }
}

Building Star Projections

KaStarTypeProjection (*) can be constructed using typeCreator.starTypeProjection:

analyze(ktFile) {
    val starProjection: KaStarTypeProjection = typeCreator.starTypeProjection()
}

27 April 2026