elastic/elasticsearch · error · ClassCastException

Cannot apply [+] operation to type [boolean]

Error message

Cannot apply [+] operation to type [boolean]

What it means

Unary plus (+) is defined for all numeric types but not for boolean. DefMath's boolean overload for plus() throws a ClassCastException when a def variable resolves to Boolean and the unary + operator is applied.

Source

Thrown at modules/lang-painless/src/main/java/org/elasticsearch/painless/DefMath.java:130

    private static int plus(int v) {
        return +v;
    }

    private static long plus(long v) {
        return +v;
    }

    private static float plus(float v) {
        return +v;
    }

    private static double plus(double v) {
        return +v;
    }

    private static boolean plus(boolean v) {
        throw new ClassCastException("Cannot apply [+] operation to type [boolean]");
    }

    private static Object plus(final Object unary) {
        if (unary instanceof Double) {
            return +(double) unary;
        } else if (unary instanceof Long) {
            return +(long) unary;
        } else if (unary instanceof Integer) {
            return +(int) unary;
        } else if (unary instanceof Float) {
            return +(float) unary;
        } else if (unary instanceof Short) {
            return +(short) unary;
        } else if (unary instanceof Character) {
            return +(char) unary;
        } else if (unary instanceof Byte) {
            return +(byte) unary;
        }

View on GitHub (pinned to db6a809a66)

Solutions

1. Verify the operand is numeric before applying unary +.
2. Use an explicit numeric type declaration instead of def.
3. Remove the unary + if it was not intended, or guard with instanceof.

Example fix

// before
def x = doc['flag'].value;
def y = +x;

// after
def x = doc['flag'].value;
if (x instanceof Number) {
    def y = +(int) x;
}

// Painless: ensure the value is numeric before unary plus
def x = doc['flag'].value;
if (x instanceof Number) {
    def y = +(int) x;
}

// Painless type guard for numeric types
def isNumeric(def value) {
    return value instanceof Number;
}

When it happens

Trigger: A Painless script applies unary + to a def variable holding a Boolean. Example: `def x = true; def y = +x;`

Common situations: Rarely intentional; usually results from a def variable whose type was inferred from runtime data that happened to be a boolean flag, combined with an expression that uses unary + as a no-op coercion.

Related errors

• Cannot apply [-] operation to type [boolean]
• Cannot apply [-] operation to type [{}].
• Cannot apply [+] operation to type [{}].
• Cannot apply [*] operation to type [boolean]
• Cannot apply [/] operation to type [boolean]

AI-assisted analysis of elastic/elasticsearch@db6a809a66 (2026-08-12). Data as JSON: /api/errors/53df9b0eb4fd1cf2. Report an issue: GitHub.