Static CIDetectorSmile 

pub unsafe static CIDetectorSmile: &'static NSString

Available on crate feature CIDetector only.

A dictionary key that configures a Core Image face feature detection operation to perform additional processing to recognize smiles in detected faces.

This option is used with /CIDetector/featuresInImage:options:

If the value of the key is true, then facial expressions such as blinking and smiles eyes are extracted. This is needed for the /CIFaceFeature/hasSmile-property to function.

See also Apple’s documentation