This is how you can use font features in Swift.

FontFeatures.swift

public static let book: Font = {
        // Font features
        let fontFeatureSettings: [CFDictionary] = [
            [
                kCTFontFeatureTypeIdentifierKey:     kTypographicExtrasType,
                kCTFontFeatureSelectorIdentifierKey: kSlashedZeroOnSelector
            ] as CFDictionary
        ]
        
        // Font description
        let fontDescriptor = CTFontDescriptorCreateWithAttributes([
            kCTFontFeatureSettingsAttribute: fontFeatureSettings
        ] as CFDictionary)
        
        let font = CTFontCreateWithName("SuisseIntl-Book" as CFString, 18, nil)
        let fontWithFeatures = CTFontCreateCopyWithAttributes(font, 18, nil, fontDescriptor)
        
        return Font(fontWithFeatures)
    }()