nushell/crates/nu-command
Ian Manske 4d3283e235
Change append operator to concatenation operator (#14344)
# Description

The "append" operator currently serves as both the append operator and
the concatenation operator. This dual role creates ambiguity when
operating on nested lists.

```nu
[1 2] ++ 3     # appends a value to a list [1 2 3]
[1 2] ++ [3 4] # concatenates two lists    [1 2 3 4]

[[1 2] [3 4]] ++ [5 6]
# does this give [[1 2] [3 4] [5 6]]
# or             [[1 2] [3 4] 5 6]  
```

Another problem is that `++=` can change the type of a variable:
```nu
mut str = 'hello '
$str ++= ['world']
($str | describe) == list<string>
```

Note that appending is only relevant for lists, but concatenation is
relevant for lists, strings, and binary values. Additionally, appending
can be expressed in terms of concatenation (see example below). So, this
PR changes the `++` operator to only perform concatenation.

# User-Facing Changes

Using the `++` operator with a list and a non-list value will now be a
compile time or runtime error.
```nu
mut list = []
$list ++= 1 # error
```
Instead, concatenate a list with one element:
```nu
$list ++= [1]
```
Or use `append`:
```nu
$list = $list | append 1
```

# After Submitting

Update book and docs.

---------

Co-authored-by: Douglas <32344964+NotTheDr01ds@users.noreply.github.com>
2024-11-24 10:59:54 -08:00
..
src Change append operator to concatenation operator (#14344) 2024-11-24 10:59:54 -08:00
tests Change append operator to concatenation operator (#14344) 2024-11-24 10:59:54 -08:00
Cargo.toml remove terminal_size crate everywhere it makes sense (#14423) 2024-11-23 19:37:12 -08:00
LICENSE Fix rest of license year ranges (#8727) 2023-04-04 09:03:29 +12:00
README.md Add top-level crate documentation/READMEs (#12907) 2024-07-14 10:10:41 +02:00

This crate contains the majority of our commands

We allow ourselves to move some of the commands in nu-command to nu-cmd-* crates as needed.

Internal Nushell crate

This crate implements components of Nushell and is not designed to support plugin authors or other users directly.