(u: unknown): u is Channel<
unknown,
unknown,
unknown,
unknown,
unknown,
unknown,
unknown
>Checks whether a value is a Channel.
Example (Checking for channels)
import { Channel } from "effect"
const channel = Channel.succeed(42)
console.log(Channel.isChannel(channel)) // true
console.log(Channel.isChannel("not a channel")) // falseexport const const isChannel: (
u: unknown
) => u is Channel<
unknown,
unknown,
unknown,
unknown,
unknown,
unknown,
unknown
>
Checks whether a value is a Channel.
Example (Checking for channels)
import { Channel } from "effect"
const channel = Channel.succeed(42)
console.log(Channel.isChannel(channel)) // true
console.log(Channel.isChannel("not a channel")) // false
isChannel = (
u: unknownu: unknown
): u: unknownu is interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<unknown, unknown, unknown, unknown, unknown, unknown, unknown> => hasProperty<"~effect/Channel">(self: unknown, property: "~effect/Channel"): self is { [K in "~effect/Channel"]: unknown; } (+1 overload)Checks whether a value has a given property key.
When to use
Use when you need a Predicate guard for property access on unknown
values with a simple structural object check.
Details
Uses the in operator and isObjectKeyword. This does not check property
value types.
Example (Guarding object properties)
import { Predicate } from "effect"
const hasName = Predicate.hasProperty("name")
const data: unknown = { name: "Ada" }
if (hasName(data)) {
console.log(data.name)
}
hasProperty(u: unknownu, const TypeId: TypeIdString literal type used as the unique brand for Channel values.
Runtime identifier stored on Channel values and used by isChannel to
recognize them.
TypeId)