nushell/src/commands/last.rs
Yehuda Katz f70c6d5d48 Extract nu_source into a crate
This commit extracts Tag, Span, Text, as well as source-related debug
facilities into a new crate called nu_source.

This change is much bigger than one might have expected because the
previous code relied heavily on implementing inherent methods on
`Tagged<T>` and `Spanned<T>`, which is no longer possible.

As a result, this change creates more concrete types instead of using
`Tagged<T>`. One notable example: Tagged<Value> became Value, and Value
became UntaggedValue.

This change clarifies the intent of the code in many places, but it does
make it a big change.
2019-11-25 07:37:33 -08:00

61 lines
1.4 KiB
Rust

use crate::commands::WholeStreamCommand;
use crate::errors::ShellError;
use crate::parser::CommandRegistry;
use crate::prelude::*;
use nu_source::Tagged;
pub struct Last;
#[derive(Deserialize)]
pub struct LastArgs {
rows: Option<Tagged<u64>>,
}
impl WholeStreamCommand for Last {
fn name(&self) -> &str {
"last"
}
fn signature(&self) -> Signature {
Signature::build("last").optional(
"rows",
SyntaxShape::Number,
"starting from the back, the number of rows to return",
)
}
fn usage(&self) -> &str {
"Show only the last number of rows."
}
fn run(
&self,
args: CommandArgs,
registry: &CommandRegistry,
) -> Result<OutputStream, ShellError> {
args.process(registry, last)?.run()
}
}
fn last(LastArgs { rows }: LastArgs, context: RunnableContext) -> Result<OutputStream, ShellError> {
let stream = async_stream! {
let v: Vec<_> = context.input.into_vec().await;
let rows_desired = if let Some(quantity) = rows {
*quantity
} else {
1
};
let count = (rows_desired as usize);
if count < v.len() {
let k = v.len() - count;
for x in v[k..].iter() {
let y: Value = x.clone();
yield ReturnSuccess::value(y)
}
}
};
Ok(stream.to_output_stream())
}