excerpt of decode.go code

decode1.go

// lines 559-583 in decode.go in encoding/json package
var f *field
fields := cachedTypeFields(v.Type())
for i := range fields {
	ff := &fields[i]
	if bytes.Equal(ff.nameBytes, key) {
		f = ff
		break
	}
	if f == nil && ff.equalFold(ff.nameBytes, key) {
		f = ff
	}
}
if f != nil {
	subv = v
	destring = f.quoted
	for _, i := range f.index {
		if subv.Kind() == reflect.Ptr {
			if subv.IsNil() {
				subv.Set(reflect.New(subv.Type().Elem()))
			}
			subv = subv.Elem()
		}
		subv = subv.Field(i)
	}
}