@Override
    public DataType setOutputType(DataType outputType, TypeContext context) {
        super.setOutputType(outputType, context);
        if (outputType != null && ! isHashCompatible(outputType))
            throw new VerificationException(this, "An " + outputType.getName() +
                                                  " output is required, but this produces int or long");
        return DataType.STRING;
    }
Hashes a string value to a long or int (by type inference on the target value).

@author bratseth
indexinglanguage/src/main/java/com/yahoo/vespa/indexinglanguage/expressions/HashExpression.java