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Typed workflows

Added in version 26.04

Typed workflows let you declare the types of a named workflow's inputs and outputs in its take: and emit: sections. Nextflow uses the annotations to validate the values that enter and leave the workflow against their declared types.

nextflow.enable.types = true

workflow hello_bye {
    take:
    samples: Channel<Path>

    main:
    ch_hello = hello(samples)
    val_bye = bye(ch_hello.collect())

    emit:
    result: Value<Path> = val_bye
}

In the above example, hello_bye takes a channel of files (Channel<Path>) and emits a dataflow value with a single file (Value<Path>).

Typed workflows require the nextflow.enable.types feature flag. For an overview of static typing and how to enable it, see Static typing. For the complete syntax reference, see Workflow (typed).

Supported types​

Channels and values are modeled using the dataflow types:

  • Use Channel<V> for a channel of values.
  • Use Value<V> for a single dataflow value.

The element type V can be any standard type, such as Path, String, or a record.

Workflow inputs can be channels, dataflow values, or regular values. Workflow outputs can be channels or dataflow values.

Restricted syntax​

The following syntax patterns are no longer supported in typed workflows:

  • Using Channel to access channel factories (use channel instead)

  • Using implicit closure parameters (declare parameters explicitly instead)

  • Using set or tap to assign channels (use standard assignments instead)

  • Composing dataflow logic with | and & (use standard method calls instead)

  • Accessing process and workflow outputs via .out (use standard assignments instead)

For more information about preparing existing code, see Preparing for static typing.

Operators​

The operator library supports static typing and records. All operators work in both typed and legacy workflows, but only a core subset of operators is recommended for static typing.

For more information about best practices when migrating existing code, see Using operators with static typing.

Validation​

The language server validates each workflow input and output against its declared type. Calling a workflow with an argument whose type does not match its take: declaration, or emitting a value that does not match its emit: declaration, is reported as an error before the pipeline runs.

See also​

  • Static typing: Overview of static typing and how to enable it.
  • Standard types: The standard types available for annotations.
  • Operators: The core operators recommended for static typing.
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