Struct ParentState 

pub struct ParentState<'a, S>
where
    S: BuilderSpecificState,
{
    value_builder: &'a mut ValueBuilder,
    saved_value_builder_offset: usize,
    metadata_builder: &'a mut dyn MetadataBuilder,
    saved_metadata_builder_dict_size: usize,
    builder_state: S,
    finished: bool,
}

Tracks information needed to correctly finalize a nested builder.

A child builder has no effect on its parent unless/until its finalize method is called, at which point the child appends the new value to the parent. As a (desirable) side effect, creating a parent state instance captures mutable references to a subset of the parent’s fields, rendering the parent object completely unusable until the parent state goes out of scope. This ensures that at most one child builder can exist at a time.

The redundancy in value_builder and metadata_builder is because all the references come from the parent, and we cannot “split” a mutable reference across two objects (parent state and the child builder that uses it). So everything has to be here.

Fields

value_builder: &'a mut ValueBuilder

saved_value_builder_offset: usize

metadata_builder: &'a mut dyn MetadataBuilder

saved_metadata_builder_dict_size: usize

builder_state: S

finished: bool

Implementations

impl<'a, S> ParentState<'a, S>

where S: BuilderSpecificState,

pub fn new( value_builder: &'a mut ValueBuilder, metadata_builder: &'a mut dyn MetadataBuilder, builder_state: S, ) -> ParentState<'a, S>

Creates a new ParentState instance. The value and metadata builder state is checkpointed and will roll back on drop, unless Self::finish is called. The builder-specific state is governed by its own finish and rollback calls.

pub fn finish(&mut self)

Marks the insertion as having succeeded and invokes BuilderSpecificState::finish. Internal state will no longer roll back on drop.

impl<'a> ParentState<'a, ()>

pub fn variant( value_builder: &'a mut ValueBuilder, metadata_builder: &'a mut dyn MetadataBuilder, ) -> ParentState<'a, ()>

Creates a new instance suitable for a top-level variant builder (e.g. VariantBuilder). The value and metadata builder state is checkpointed and will roll back on drop, unless Self::finish is called.

impl<'a> ParentState<'a, ListState<'a>>

pub fn list( value_builder: &'a mut ValueBuilder, metadata_builder: &'a mut dyn MetadataBuilder, offsets: &'a mut Vec<usize>, saved_parent_value_builder_offset: usize, ) -> ParentState<'a, ListState<'a>>

Creates a new instance suitable for a ListBuilder. The value and metadata builder state is checkpointed and will roll back on drop, unless Self::finish is called. The new element’s offset is also captured eagerly and will also roll back if not finished.

impl<'a> ParentState<'a, ObjectState<'a>>

pub fn try_object( value_builder: &'a mut ValueBuilder, metadata_builder: &'a mut dyn MetadataBuilder, fields: &'a mut IndexMap<u32, usize>, saved_parent_value_builder_offset: usize, field_name: &str, validate_unique_fields: bool, ) -> Result<ParentState<'a, ObjectState<'a>>, ArrowError>

Creates a new instance suitable for an ObjectBuilder. The value and metadata builder state is checkpointed and will roll back on drop, unless Self::finish is called. The new field’s name and offset are also captured eagerly and will also roll back if not finished.

The call fails if the field name is invalid (e.g. because it duplicates an existing field).

Trait Implementations

impl<'a, S> Debug for ParentState<'a, S>

where S: Debug + BuilderSpecificState,

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

Formats the value using the given formatter.

impl<S> Drop for ParentState<'_, S>

where S: BuilderSpecificState,

Automatically rolls back any unfinished ParentState.

fn drop(&mut self)

Executes the destructor for this type.