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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>
Nushell core libraries and plugins
These sub-crates form both the foundation for Nu and a set of plugins which extend Nu with additional functionality.
Foundational libraries are split into two kinds of crates:
- Core crates - those crates that work together to build the Nushell language engine
- Support crates - a set of crates that support the engine with additional features like JSON support, ANSI support, and more.
Plugins are likewise also split into two types:
- Core plugins - plugins that provide part of the default experience of Nu, including access to the system properties, processes, and web-connectivity features.
- Extra plugins - these plugins run a wide range of different capabilities like working with different file types, charting, viewing binary data, and more.