STRING_8 does not conform to STRING_UC in is_equal

I'm trying to build xplain2sql using Gobo compiler and its tools. After issuing geant compile command I get a lot of similar errors:

[CATCALL] class SQL_GENERATOR_TSQL65 (SQL_GENERATOR,2610,5): type 'STRING_8' of actual argument #1 does not conform to type 'UC_STRING' of formal argument in feature `is_equal' in class 'UC_STRING'

Above error refers to the last line of this code:

    sql_infix_expression (a_left: XPLAIN_EXPRESSION; an_operator: STRING; a_right: XPLAIN_EXPRESSION): STRING
        -- SQL expression for multiplication/division, etc.
    require
        valid_left: a_left /= Void
        valid_right: a_right /= Void
        operator_not_empty: an_operator /= Void and then not an_operator.is_empty
    local
        left_value,
        right_value: STRING
    do
        if
            an_operator.is_equal (once "+") and then

I don't know Eiffel, I just want to compile this code. There were other build errors which I was able to fix using some common sense and experience from other programming languages but I don't know how to deal with this.

Solution

In this case, I think you could use same_string (..) as replacement for is_equal (..) .