presto-main/src/main/java/io/prestosql/metadata/TypeVariableConstraint.java/TypeVariableConstraint/toString
class TypeVariableConstraint:    @Override
    public String toString()
    {
        String value = name;
        if (comparableRequired) {
            value += ":comparable";
        }
        if (orderableRequired) {
            value += ":orderable";
        }
        if (variadicBound != null) {
            value += ":" + variadicBound + "<*>";
        }
        if (!castableTo.isEmpty()) {
            value += ":castableTo(" + Joiner.on(", ").join(castableTo) + ")";
        }
        if (!castableFrom.isEmpty()) {
            value += ":castableFrom(" + Joiner.on(", ").join(castableFrom) + ")";
        }
        return value;
    }