default value. It is used when ASDF value equals Asdf.init.
cast(T) this if this != Asdf.init and def otherwise.
import asdf.jsonparser; auto asdfData = `{"foo":"bar","inner":{"a":true,"b":false,"c":"32323","d":null,"e":{}}}`.parseJson; assert(asdfData["inner", "a"].get(false) == true); assert(asdfData["inner", "b"].get(true) == false); assert(asdfData["inner", "c"].get(100) == 32323); assert(asdfData["no", "such", "keys"].get(100) == 100);