Enum PreviousDescription 

pub enum PreviousDescription<'a> {
    Resolve,
    Absent,
    Id(&'a str),
}

The description a Groups::set_description call expects to replace.

The server takes the prev attribute as an optimistic-concurrency token: it applies the update only when the token matches the group’s current description id, and answers 409 conflict otherwise. A group with no description expects no token at all.

The default is PreviousDescription::Resolve because it is the only variant that is correct without knowing anything about the group. Note that it is also the only one that costs a round trip.

Variants

Resolve

Read the group’s current description id from the server before sending. The right choice when the caller holds no fresh metadata.

Absent

The group carries no description yet (a freshly created group), so no token is sent.

Id(&'a str)

A description id the caller already holds, typically GroupMetadata::description_id from a recent Groups::get_metadata.

Trait Implementations

impl<'a> Clone for PreviousDescription<'a>

fn clone(&self) -> PreviousDescription<'a>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<'a> Copy for PreviousDescription<'a>

impl<'a> Debug for PreviousDescription<'a>

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

Formats the value using the given formatter.

impl<'a> Default for PreviousDescription<'a>

fn default() -> PreviousDescription<'a>

Returns the “default value” for a type.

impl<'a> Eq for PreviousDescription<'a>

impl<'a> From<Option<&'a str>> for PreviousDescription<'a>

Turns a held GroupMetadata::description_id into a token.

None means “that metadata says the group has no description”, so it maps to PreviousDescription::Absent and not to a fresh read. Metadata stale enough to have missed a description added since is therefore answered with GroupError::DescriptionConflict; pass PreviousDescription::Resolve when the age of the metadata is unknown.

fn from(description_id: Option<&'a str>) -> Self

Converts to this type from the input type.

impl<'a> PartialEq for PreviousDescription<'a>

fn eq(&self, other: &PreviousDescription<'a>) -> bool

Equality operator ==.

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

Inequality operator !=.

impl<'a> StructuralPartialEq for PreviousDescription<'a>