apple/pkl · error · VmException

cannotInstantiateType

cannotInstantiateType

Error message

Cannot instantiate type `{0}`.

What it means

Pkl throws `cannotInstantiateType` when `new Type { ... }` names a type that cannot be instantiated — abstract classes, type aliases to non-instantiable types, modules, etc. AbstractInferParentNode.getDefaultValue falls through to this error after the more specific checks fail, including the source text of the type in the message.

Source

Thrown at pkl-core/src/main/java/org/pkl/core/ast/expression/member/AbstractInferParentNode.java:65

    var defaultValue = typeNode.createDefaultValue(frame, language, headerSection, qualifiedName);
    if (defaultValue != null) {
      return defaultValue;
    }

    CompilerDirectives.transferToInterpreter();

    if (typeNode instanceof TypeVariableNode) {
      throw exceptionBuilder().evalError("cannotInferParent").build();
    }

    // try to produce a more specific error message than "cannotInstantiateType"
    var clazz = typeNode.getVmClass();
    if (clazz != null) {
      VmUtils.checkIsInstantiable(clazz, typeNode);
    }

    throw exceptionBuilder()
        .evalError("cannotInstantiateType", typeNode.getSourceSection().getCharacters())
        .build();
  }
}

View on GitHub (pinned to f3efcbfc9b)

Solutions

1. Replace the type with a concrete, non-abstract class that can be instantiated.
2. If the type is a union/alias, instantiate one of its concrete members instead.
3. Use `amend` semantics (`parent { ... }`) rather than `new` when extending an existing object.

Example fix

// before
new AbstractServer { port = 8080 } // abstract
// after
new HttpServer {
  port = 8080
}

// Pkl
// ensure the type is a concrete class before `new`
// new ConcreteClass { ... }  // OK; new AbstractThing { ... } fails

When it happens

Trigger: `new` applied to an abstract/open class, a module, a union or constrained type where no concrete class is resolvable; typeNode.getVmClass() is null or VmUtils.checkIsInstantiable rejects it.

Common situations: `new` on base types like `Int`/`String`-constrained aliases, on abstract base classes meant for inheritance only, or on module types after a refactor.

Related errors

• cannotInstantiateAbstractClass
• cannotFindMember
• cannotInstantiateExternalClass
• invalidSupertype
• invalidTypeName

AI-assisted analysis of apple/pkl@f3efcbfc9b (2026-09-08). Data as JSON: /api/errors/37c694c12fe48b23. Report an issue: GitHub.