Private / public constructors in DTO coherence

[darkspock]

In the example PostCheepCommand, you use a private constructor, in SignUpCommand a public constructor, later a named constructor.
I know the reader should know the difference and when to use it, but is confusing to follow the examples this way.
I think should explain the benefits and tradeoff of fromArray, because in the example is contrary to the phrase in the same chapter "It will also add type safety and IDE assistance, too."

Filling from array is not type safety and the IDE can not help.