Method decode

arrow-json/src/reader/map_array.rs:85–155

(&mut self, tape: &Tape<'_>, pos: &[u32])

impl ArrayDecoder for MapArrayDecoder {
    fn decode(&mut self, tape: &Tape<'_>, pos: &[u32]) -> Result<ArrayRef, ArrowError> {
        let mut offsets = BufferBuilder::<i32>::new(pos.len() + 1);
        offsets.append(0);

        let mut key_pos = Vec::with_capacity(pos.len());
        let mut value_pos = Vec::with_capacity(pos.len());

        let mut nulls = self.is_nullable.then(|| NullBufferBuilder::new(pos.len()));

        for p in pos.iter().copied() {
            let end_idx = match (tape.get(p), nulls.as_mut()) {
                (TapeElement::StartObject(end_idx), None) => end_idx,
                (TapeElement::StartObject(end_idx), Some(nulls)) => {
                    nulls.append_non_null();
                    end_idx
                }
                (TapeElement::Null, Some(nulls)) => {
                    nulls.append_null();
                    p + 1
                }
                (_, Some(nulls)) if self.ignore_type_conflicts => {
                    nulls.append_null();
                    p + 1
                }
                _ => return Err(tape.error(p, "{")),
            };

            let mut cur_idx = p + 1;
            while cur_idx < end_idx {
                let key = cur_idx;
                let value = tape.next(key, "map key")?;
                cur_idx = tape.next(value, "map value")?;

                key_pos.push(key);
                value_pos.push(value);
            }

            let offset = i32::from_usize(key_pos.len()).ok_or_else(|| {
                ArrowError::JsonError("offset overflow decoding MapArray".to_string())
            })?;
            offsets.append(offset)
        }

        assert_eq!(key_pos.len(), value_pos.len());

        let key_array = self.keys.decode(tape, &key_pos)?;
        let value_array = self.values.decode(tape, &value_pos)?;

        // SAFETY: fields/arrays match the schema, lengths are equal, no nulls
        let entries = unsafe {
            StructArray::new_unchecked_with_length(
                self.key_value_fields.clone(),
                vec![key_array, value_array],
                None,
                key_pos.len(),
            )
        };