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# Description
While working on something else, I noticed that
`Value::follow_cell_path` receives `self`.
While it would be ideal for the signature to be `(&'a self, cell_path)
-> &'a Value`, that's not possible because:
1. Selecting a row from a list and field from a record can be done with
a reference but selecting a column from a table requires creating a new
list.
2. `Value::Custom` returns new `Value`s when indexed.
So the signature becomes `(&'a self, cell_path) -> Cow<'a, Value>`.
Another complication that arises is, once a new `Value` is created, and
it is further indexed, the `current` variable
1. can't be `&'a Value`, as the lifetime requirement means it can't
refer to local variables
2. _shouldn't_ be `Cow<'a, Value>`, as once it becomes an owned value,
it can't be borrowed ever again, as `current` is derived from its
previous value in further iterations. So once it's owned, it can't be
indexed by reference, leading to more clones
We need `current` to have _two_ possible lifetimes
1. `'out`: references derived from `&self`
2. `'local`: references derived from an owned value stored in a local
variable
```rust
enum MultiLife<'out, 'local, T>
where
'out: 'local,
T: ?Sized,
{
Out(&'out T),
Local(&'local T),
}
```
With `current: MultiLife<'out, '_, Value>`, we can traverse values with
minimal clones, and we can transform it to `Cow<'out, Value>` easily
(`MultiLife::Out -> Cow::Borrowed, MultiLife::Local -> Cow::Owned`) to
return it
# User-Facing Changes
# Tests + Formatting
# After Submitting
---------
Co-authored-by: Bahex <17417311+Bahex@users.noreply.github.com>
nu-cmd-extra
The commands in this crate are the extra commands of Nushell. These commands are not in a state to be guaranteed to be part of the 1.0 API; meaning that there is no guarantee longer term that these commands will be around into the future.
For a while we did exclude them behind the --features extra compile time
flag, meaning that the default release did not contain them. As we (the Nushell
team) shipped a full build including both extra and dataframe for some
time, we chose to sunset the extra feature but keep the commands in this
crate for now. In the future the commands may be moved to more topical crates
or discarded into plugins.