Enum nu_protocol::PipelineData

pub enum PipelineData {
    Value(Value, Option<PipelineMetadata>),
    ListStream(ListStream, Option<PipelineMetadata>),
    ExternalStream {
        stdout: Option<RawStream>,
        stderr: Option<RawStream>,
        exit_code: Option<ListStream>,
        span: Span,
        metadata: Option<PipelineMetadata>,
    },
}

The foundational abstraction for input and output to commands

This represents either a single Value or a stream of values coming into the command or leaving a command.

A note on implementation:

We’ve tried a few variations of this structure. Listing these below so we have a record.

• We tried always assuming a stream in Nushell. This was a great 80% solution, but it had some rough edges. Namely, how do you know the difference between a single string and a list of one string. How do you know when to flatten the data given to you from a data source into the stream or to keep it as an unflattened list?

• We tried putting the stream into Value. This had some interesting properties as now commands “just worked on values”, but lead to a few unfortunate issues.

The first is that you can’t easily clone Values in a way that felt largely immutable. For example, if you cloned a Value which contained a stream, and in one variable drained some part of it, then the second variable would see different values based on what you did to the first.

To make this kind of mutation thread-safe, we would have had to produce a lock for the stream, which in practice would have meant always locking the stream before reading from it. But more fundamentally, it felt wrong in practice that observation of a value at runtime could affect other values which happen to alias the same stream. By separating these, we don’t have this effect. Instead, variables could get concrete list values rather than streams, and be able to view them without non-local effects.

• A balance of the two approaches is what we’ve landed on: Values are thread-safe to pass, and we can stream them into any sources. Streams are still available to model the infinite streams approach of original Nushell.

Variants

Value(Value, Option<PipelineMetadata>)

ListStream(ListStream, Option<PipelineMetadata>)

ExternalStream

Fields

stdout: Option<RawStream>

stderr: Option<RawStream>

exit_code: Option<ListStream>

span: Span

metadata: Option<PipelineMetadata>

Implementations

impl PipelineData

pub fn new(span: Span) -> PipelineData

pub fn new_with_metadata(
    metadata: Option<PipelineMetadata>,
    span: Span
) -> PipelineData

pub fn metadata(&self) -> Option<PipelineMetadata>

pub fn set_metadata(self, metadata: Option<PipelineMetadata>) -> Self

pub fn is_nothing(&self) -> bool

pub fn into_value(self, span: Span) -> Value

pub fn into_interruptible_iter(
    self,
    ctrlc: Option<Arc<AtomicBool>>
) -> PipelineIterator

pub fn collect_string(
    self,
    separator: &str,
    config: &Config
) -> Result<String, ShellError>

pub fn follow_cell_path(
    self,
    cell_path: &[PathMember],
    head: Span,
    insensitive: bool
) -> Result<Value, ShellError>

pub fn upsert_cell_path(
    &mut self,
    cell_path: &[PathMember],
    callback: Box<dyn FnOnce(&Value) -> Value>,
    head: Span
) -> Result<(), ShellError>

pub fn map<F>(
    self,
    f: F,
    ctrlc: Option<Arc<AtomicBool>>
) -> Result<PipelineData, ShellError> where
    Self: Sized,
    F: FnMut(Value) -> Value + 'static + Send, 

Simplified mapper to help with simple values also. For full iterator support use .into_iter() instead

pub fn flat_map<U: 'static, F>(
    self,
    f: F,
    ctrlc: Option<Arc<AtomicBool>>
) -> Result<PipelineData, ShellError> where
    Self: Sized,
    U: IntoIterator<Item = Value>,
    <U as IntoIterator>::IntoIter: 'static + Send,
    F: FnMut(Value) -> U + 'static + Send, 

Simplified flatmapper. For full iterator support use .into_iter() instead

pub fn filter<F>(
    self,
    f: F,
    ctrlc: Option<Arc<AtomicBool>>
) -> Result<PipelineData, ShellError> where
    Self: Sized,
    F: FnMut(&Value) -> bool + 'static + Send, 

pub fn print(
    self,
    engine_state: &EngineState,
    stack: &mut Stack,
    no_newline: bool,
    to_stderr: bool
) -> Result<(), ShellError>

Consume and print self data immediately.

no_newline controls if we need to attach newline character to output. to_stderr controls if data is output to stderr, when the value is false, the data is ouput to stdout.

Trait Implementations

impl Debug for PipelineData

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl IntoIterator for PipelineData

type Item = Value

The type of the elements being iterated over.

type IntoIter = PipelineIterator

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.