# Description
This changes the default behaviour of `let` to be able to take a
pipeline as its initial value.
For example:
```
> let x = "hello world" | str length
```
This is a change from the existing behaviour, where the right hand side
is assumed to be an expression. Pipelines are more general, and can be
more powerful.
My google foo is failing me, but this also fixes this issue:
```
let x = foo
```
Currently, this reads `foo` as a bareword that gets converted to a
string rather than running the `foo` command. In practice, this is
really annoying and is a really hard to spot bug in a script.
# User-Facing Changes
BREAKING CHANGE BREAKING CHANGE
`let` gains the power to be assigned via a pipeline. However, this
changes the behaviour of `let x = foo` from assigning the string "foo"
to `$x` to being "run the command `foo` and give the result to `$x`"
# Tests + Formatting
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Don't forget to add tests that cover your changes.
Make sure you've run and fixed any issues with these commands:
- `cargo fmt --all -- --check` to check standard code formatting (`cargo
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- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect -A clippy::result_large_err` to check that
you're using the standard code style
- `cargo test --workspace` to check that all tests pass
- `cargo run -- crates/nu-std/tests/run.nu` to run the tests for the
standard library
> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
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> toolkit check pr
> ```
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# After Submitting
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# Description
this pr condenses `MutBuiltinVar`, `LetBuiltinVar` and `ConstBuiltinVar`
into one error:
```nu
Error: nu::parser::name_is_builtin_var
× `in` used as variable name.
╭─[entry #69:1:1]
1 │ let in = 420
· ─┬
· ╰── already a builtin variable
╰────
help: 'in' is the name of a builtin Nushell variable and cannot be used
as a variable name
```
it also fixes this case which was previously not handled
```nu
let $nu = 420 # this variable would have been 'lost'
```
# Description
Fixes: #8136
# User-Facing Changes
The following command
```
let VAR = ^cat non-existing-file; echo "failed"
```
will no longer output `failed` message
# Tests + Formatting
Don't forget to add tests that cover your changes.
Make sure you've run and fixed any issues with these commands:
- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass
# After Submitting
If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.
---------
Co-authored-by: Reilly Wood <reilly.wood@icloud.com>
This adds support for (limited) mutable variables. Mutable variables are created with mut much the same way immutable variables are made with let.
Mutable variables allow mutation via the assignment operator (=).
❯ mut x = 100
❯ $x = 200
❯ print $x
200
Mutable variables are limited in that they're only tended to be used in the local code block. Trying to capture a local variable will result in an error:
❯ mut x = 123; {|| $x }
Error: nu::parser::expected_keyword (link)
× Capture of mutable variable.
The intent of this limitation is to reduce some of the issues with mutable variables in general: namely they make code that's harder to reason about. By reducing the scope that a mutable variable can be used it, we can help create local reasoning about them.
Mutation can occur with fields as well, as in this case:
❯ mut y = {abc: 123}
❯ $y.abc = 456
❯ $y
On a historical note: mutable variables are something that we resisted for quite a long time, leaning as much as we could on the functional style of pipelines and dataflow. That said, we've watched folks struggle to work with reduce as an approximation for patterns that would be trivial to express with local mutation. With that in mind, we're leaning towards the happy path.
