elastic/elasticsearch · error · IllegalArgumentException

function reference [ ::new/ ] matching [ , / ] not found

Error message

function reference [%s::new/%d] matching [%s, %s/%d] not found

What it means

FunctionRef.create throws this IllegalArgumentException at compile time when a constructor reference 'Type::new' cannot resolve a whitelisted Painless constructor with the required argument count. The compiler calls lookupPainlessConstructor(typeName, interfaceTypeParametersSize); if null, no constructor of that class taking exactly that many parameters is registered in the Painless allowlist. Constructor references in Painless can only target classes and constructors explicitly whitelisted.

Solutions

1. Confirm the class is whitelisted for construction in Painless (check the allowed classes list).
2. Adjust the functional interface so its parameter count matches a whitelisted constructor arity.
3. Replace the constructor reference with an explicit lambda that calls the constructor with the correct arguments.

Example fix

// before
Function<String, StringBuilder> f = StringBuilder::new;  // if String-arg ctor not whitelisted
// after
Supplier<StringBuilder> f = StringBuilder::new;  // use no-arg ctor

// Confirm the class is whitelisted and has a constructor with matching arity:
// // Check Painless allowed classes list for the target class and constructor

When it happens

Trigger: Writing 'HashMap::new' or 'StringBuilder::new' where the class is not whitelisted, or the constructor arity does not match the functional interface's parameter count. For example, 'Supplier<List> s = ArrayList::new;' works (no-arg constructor) but 'Function<Integer, ArrayList> f = ArrayList::new;' fails if the single-int-arg constructor is not whitelisted.

Common situations: Referencing a Java class not permitted in Painless scripts. Mismatched constructor arity between the functional interface and available constructors. Class present in Java but absent from the Painless whitelist.

Related errors

• function reference [ :: / ] matching [ , / ] not found
• Cannot apply operator
• Cannot apply operator
• Cannot cast to
• cannot convert function reference

AI-assisted analysis of elastic/elasticsearch@db6a809a66 (2026-08-12). Data as JSON: /api/errors/8c83f5070ed2b7ef. Report an issue: GitHub.

Appendix: source

Thrown at modules/lang-painless/src/main/java/org/elasticsearch/painless/FunctionRef.java:146

                delegateClassName = CLASS_NAME;
                isDelegateInterface = false;
                isDelegateAugmented = false;
                delegateInvokeType = needsScriptInstance ? H_INVOKEVIRTUAL : H_INVOKESTATIC;
                delegateMethodName = localFunction.getMangledName();
                delegateMethodType = localFunction.getMethodType();
                delegateInjections = new Object[0];

                delegateMethodReturnType = localFunction.getReturnType();
                delegateMethodParameters = localFunction.getTypeParameters();
            } else if ("new".equals(methodName)) {
                if (numberOfCaptures != 0) {
                    throw new IllegalStateException("internal error");
                }

                PainlessConstructor painlessConstructor = painlessLookup.lookupPainlessConstructor(typeName, interfaceTypeParametersSize);

                if (painlessConstructor == null) {
                    throw new IllegalArgumentException(
                        Strings.format(
                            "function reference [%s::new/%d] matching [%s, %s/%d] not found",
                            typeName,
                            interfaceTypeParametersSize,
                            targetClassName,
                            interfaceMethodName,
                            interfaceTypeParametersSize
                        )
                    );
                }

                delegateClassName = painlessConstructor.javaConstructor().getDeclaringClass().getName();
                isDelegateInterface = false;
                isDelegateAugmented = false;
                delegateInvokeType = H_NEWINVOKESPECIAL;
                delegateMethodName = PainlessLookupUtility.CONSTRUCTOR_NAME;
                delegateMethodType = painlessConstructor.methodType();
                delegateInjections = new Object[0];

View on GitHub (pinned to db6a809a66)