Read the Rust Without Guessing

You can follow the product questions without writing Rust. When a code block is useful, read its domain words first: verify identity, admit registration, record it, then handle the follow-up.

This contract says what verification can produce:

pub trait VerifyIdentity: private::Stage + Sized {
    type Registered: RecordedRegistration;
    type Verified: AdmitRegistration<Registered = Self::Registered>;
    fn verify(self) -> Result<Self::Verified, IdentityFailure>;
}

Code	Plain Meaning
`trait VerifyIdentity`	A contract that provides identity verification.
`type Verified: AdmitRegistration`	Its successful next value must support registration admission.
`Registered = Self::Registered`	The next contract preserves the declared registration-result type.
`fn verify(self)`	Calling verification consumes this submitted stage.
`Result<..., IdentityFailure>`	At runtime it returns a successful next stage or an identity failure.
`private::Stage`	Outside callers cannot freely invent implementations of this protected stage.
`Sized`	This contract uses an ordinary statically sized receiver; it does not mean a state must be zero-sized.

The declaration connects a legitimate successor. It does not say that every submitted assertion is valid.

Engineering Depth

Read a consuming chain from left to right:

shop.signup(assertion)
    .verify()?
    .admit()?
    .record()
    .into_followups()

This is a fragment inside a function whose error type can represent the declared failures. ? returns early on a failure; it does not ignore it. The reference's known-valid test consumer uses unwrap() instead. That test shorthand would be inappropriate for handling arbitrary user input in an application.

Compare two receivers:

Signature Fragment	What the Caller Retains
`fn inspect(&self)`	A borrow; the caller still owns the value.
`fn finish(self)`	Ownership moves into the call. A non-copyable value cannot then be reused.

In &'a mut Workshop, &mut is an exclusive borrow and 'a names how long that borrow can be used. It can stop local code from swapping a resource while a stage uses it. It does not lock another process or make data survive a crash.

More syntax: :: selects an associated item, . calls through a value, and <P> supplies a type parameter. Follow the glossary when a term still hides a product question.

Your Reflection

Which part says that admission is the legitimate next operation? Which part represents the possibility that the identity provider is unavailable?

Worked Discussion

The associated successor bound Verified: AdmitRegistration supplies the first relationship. Result<..., IdentityFailure> supplies the runtime alternative. The compiler can enforce the declared relationship while a real request still fails at the provider boundary.