Although there was some dispute among the earlier authorities, it is the rule today that comprehensive zoning ordinances, if enacted under proper legislative authority, are constitutional and will be upheld in so far as they are reasonable in application. In order to give aggrieved property owners an opportunity to obtain relief upon the basis of the ordinance itself without attacking its constitutionality, it has become common practice to give the board of appeals the power to vary the operation of the ordinance in specific cases.