What is the Oxidation number of Fe in FeS2?

In assigning formal oxidation states it is necessary to consider the bonding present amongst the species involved. FeS2 was one of the earliest crystal structures solved by X-ray diffraction methods and the simple cubic crystals clearly show sulphur-sulphur bonding within [S-S]2- units. These can be viewed as derived from hydrogen disulphide, H2S2 (cf. hydrogen peroxide, H2O2). Thus FeS2 would be better described as iron persulphide rather than disulphide. In considering the material as Fe2+S22− it is clear that the oxidation state of Fe is +2 while that of each S moeity is -1. A similar problem can be posed via barium peroxide, BaO2, where the oxidation state of barium must be +2 (metal in Gp 2). What is the oxidation state of oxygen in BaO2 ?