Struct Const

pub struct Const<T: Message = String> {
    pub output: OutputPort<T>,
    pub value: T,
}

A block for sending a constant value.

This block sends a constant value on its output port. It can also be used to send a constant value to multiple blocks.

The value to send is specified as a parameter, and can be of any type that implements the Message trait.

The block waits for the output port to be connected before sending the value, and closes the port after the value is sent.

The block does not have any input ports nor state.

Block Diagram

block-beta
    columns 4
    Const space:2 Sink
    Const-- "output" -->Sink

    classDef block height:48px,padding:8px;
    classDef hidden visibility:none;
    class Const block
    class Sink hidden

Sequence Diagram

sequenceDiagram
    autonumber
    participant Const as Const block
    participant Const.output as Const.output port
    participant BlockA as Another block

    Const-->>BlockA: Connect

    Const->>BlockA: Message

    Const-->>Const.output: Close
    Const-->>BlockA: Disconnect

Examples

Using the block in a system

System::build(|s| {
    let const_value = s.const_string("Hello, world!");
    let line_encoder = s.encode_lines();
    let stdout = s.write_stdout();
    s.connect(&const_value.output, &line_encoder.input);
    s.connect(&line_encoder.output, &stdout.input);
});

Running the block via the CLI

$ protoflow execute Const value=Hello

Fields

output: OutputPort<T>

The port to send the value on.

value: T

A parameter for the value to send.

Implementations

impl<T: Message + Default> Const<T>

pub fn new(output: OutputPort<T>) -> Self

impl<T: Message> Const<T>

pub fn with_params(output: OutputPort<T>, value: T) -> Self

impl<T: Message + 'static> Const<T>

pub fn with_system(system: &System, value: T) -> Self

Trait Implementations

impl<T: Message> Block for Const<T>

fn execute(&mut self, runtime: &dyn BlockRuntime) -> BlockResult

Executes this block’s computation.

fn prepare(&mut self, _runtime: &dyn BlockRuntime) -> Result<(), BlockError>

Prepares this block for execution.

impl<T: Message> BlockDescriptor for Const<T>

fn inputs(&self) -> Vec<PortDescriptor>

A description of this block’s input ports.

fn outputs(&self) -> Vec<PortDescriptor>

A description of this block’s output ports.

fn parameters(&self) -> Vec<ParameterDescriptor>

A description of this block’s parameters.

fn ports(&self) -> Vec<PortDescriptor>

A description of this block’s I/O ports.

impl<T: Clone + Message> Clone for Const<T>

fn clone(&self) -> Const<T>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Message> MaybeLabeled for Const<T>

fn label(&self) -> Option<Cow<'_, str>>

Returns the human-readable label, if any, of the object.

fn is_labeled(&self) -> bool

Checks whether the object has a human-readable label.

impl<T: Message> MaybeNamed for Const<T>

fn name(&self) -> Option<Cow<'_, str>>

Returns the name, if any, of the object.

fn is_named(&self) -> bool

Checks whether the object has a name.

impl<T: Message> StdioSystem for Const<T>

fn build_system(config: StdioConfig) -> Result<System, StdioError>