viirya opened a new pull request, #5218:
URL: https://github.com/apache/arrow-rs/pull/5218
# Which issue does this PR close?
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Closes #.
# Rationale for this change
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`MapBuilder` provides `keys` and `values` functions to get key and value
array builders of map separately. As it is mutable borrow of the map builder,
when we want to set keys and values in a loop like:
```rust
let key_builder = builder.keys();
let value_builder = builder.values();
let keys = ...;
let values = ...;
for idx in 0..keys.get_num_elements() {
let key = keys.get(idx);
let value = values.get(idx);
key_builder.append_value(key);
value_builder.append_value(value);
}
```
The compiler will complain `error[E0499]: cannot borrow `*builder` as
mutable more than once at a time`.
Although there is workaround that is to get key and value builders inside
the loop, no sure if it is efficient. More, especially we can have `Box<dyn
ArrayBuilder>` as key and value builders now, it means that we need to
`downcast` both key and value builders for each iteration in the loop.
This patch adds `keys_and_values` API to `MapBuilder` that can get both key
and value builders in one mutable borrow.
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# Are there any user-facing changes?
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