The Constructor is the EROS mechanism that tests confinement. In practice, constructors prove to be the most common means for encapsulating and fabricating programs. If I want to give you the ability to run a program, I hand you a constructor for it. None of the constructor tests rely on any notion of user identity.
Constructors Provides both certification and construction of programs.
Runs trusted code, holds non-trusted capabilities. If this test passes for all capabilities held by yield, then constructor alleges discretion.