Struct MessageFieldView 

pub struct MessageFieldView<V> { /* private fields */ }

A borrowed view of an optional message field.

Analogous to MessageField<T> but for the view layer. Like MessageField, the inner view is boxed — recursive message types (Foo { NestedMessage { corecursive: Foo } }) would otherwise have infinite size. The box is API-transparent: Deref returns &V, and set() takes V by value.

When V implements DefaultViewInstance, this type implements Deref<Target = V>, returning a reference to a static default instance when the field is unset — making view code identical to owned code for field access:

// Both work the same, regardless of whether `address` is set:
let city = owned_msg.address.city;    // MessageField<Address>
let city = view_msg.address.city;     // MessageFieldView<AddressView>

The lifetime of the contained view type V (e.g. AddressView<'a>) ties this to the input buffer — no separate lifetime parameter is needed here.

Implementations

impl<V> MessageFieldView<V>

pub const fn unset() -> Self

An unset field (the default).

pub fn set(v: V) -> Self

A set field with the given view value.

pub fn some(v: V) -> Self

Alias for set, mirroring owned MessageField::some.

pub fn is_set(&self) -> bool

Returns true if the field has a value.

pub fn is_unset(&self) -> bool

Returns true if the field has no value.

pub fn as_option(&self) -> Option<&V>

Get a reference to the inner view, or None if unset.

pub fn as_mut(&mut self) -> Option<&mut V>

Get a mutable reference to the inner view, or None if unset.

Used by generated decode code to merge a second occurrence of a message field into an existing value (proto merge semantics).

impl<'a, V: ViewEncode<'a>> MessageFieldView<V>

pub fn compute_size(&self, cache: &mut SizeCache) -> u32

Forward to the inner view’s compute_size, or 0 if unset. Generated compute_size calls this for nested-message fields, mirroring MessageField on the owned side.

pub fn write_to(&self, cache: &mut SizeCache, buf: &mut impl BufMut)

Forward to the inner view’s write_to; no-op if unset.

Trait Implementations

impl<V: Clone> Clone for MessageFieldView<V>

fn clone(&self) -> MessageFieldView<V>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<V: Debug> Debug for MessageFieldView<V>

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

Formats the value using the given formatter.

impl<V> Default for MessageFieldView<V>

fn default() -> Self

Returns the “default value” for a type.

impl<V: DefaultViewInstance> Deref for MessageFieldView<V>

type Target = V

The resulting type after dereferencing.

fn deref(&self) -> &V

Dereferences the value.

impl<V> From<V> for MessageFieldView<V>

fn from(v: V) -> Self

Converts to this type from the input type.

impl<V: PartialEq + DefaultViewInstance> PartialEq for MessageFieldView<V>

Wire-equivalent equality: Unset equals Set(v) when v equals the default instance.

This matches MessageField::eq on the owned side, so view_a == view_b agrees with view_a.to_owned_message() == view_b.to_owned_message().

The comparison against the default routes through the Deref impl.

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<V: Eq + DefaultViewInstance> Eq for MessageFieldView<V>