Enum FieldChange 

pub enum FieldChange {
    Set {
        from: String,
        to: String,
    },
    Clear {
        from: String,
    },
    NoChange {
        value: String,
    },
}

One field’s proposed change on one issue.

Variants

Set

The field would take a new value.

Fields

from: String

to: String

Clear

The field would be emptied.

Fields

from: String

NoChange

The field already holds the requested value, so nothing is written for it.

A distinct variant, not a missing entry. The data-model’s rule is “a patch that is already the requested final state is a no-op and produces no duplicate History event”, and the way that is enforced is by knowing it — a plan that merely omitted the field could not distinguish “no-op” from “not considered”, and the History intent below depends on the difference.

Fields

value: String

Implementations

impl FieldChange

pub fn field(&self) -> &'static str

The name of the field, for a rendering line.

pub fn writes(&self) -> bool

Whether this change writes anything.

pub fn as_from_to(&self) -> (String, String)

The change as (from, to), for a surface that projects a plan to a structured value.

A method rather than a match in each surface, for the same reason ItemOutcome::status is one: surface-parity.md §2 requires every surface to expose the same “proposed before/after values”, and three matches over these variants is three places for a fourth surface — or a new variant — to disagree about what a Clear’s to is.

Clear’s to is the empty string, not null and not a missing key, so a client reading to unconditionally gets a string for every field. A NoChange reports from == to, which is the truth: the value would not move.

Trait Implementations

impl Clone for FieldChange

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for FieldChange

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for FieldChange

impl PartialEq for FieldChange

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for FieldChange