CODEWITHSUNDEEP
go
juanleon
juanleon

Reputation: 9380

go: how to pass directional channels to a function accepting bidirectional channel?

Hi have a function accepting chan []byte (that, since no direction is specified I understand it is bidirectional). The function does not send or receives anything, only looks at number of elements in the channel for stats related purposes.

I want to call this function within a function with following signature:

func foo(fooChannel chan<- []byte)

But when I try to use argument to call the other function I got the error cannot use fooChannel (type <-chan []byte) as type chan []byte in function argument.

Is there any way to cast fooChannel to chan []byte?

Since I am only interested in getting some stats, how should I prototype the function to accept any type of channel (so I can get rid even of the "byte" part)? I am only using len and cap with channels received as arguments.

Upvotes: 3

Views: 1484

Answers (2)

tomasz
tomasz

Reputation: 13072

Is there any way to cast fooChannel to chan []byte?

No, sorry. This is probably just in case someone thinks they would like to send on the receiving channel anyway. But, just a little tiny thing, but... No.

The function does not send or receives anything, only looks at number of elements in the channel for stats related purposes. [...] I am only using len and cap with channels received as arguments.

If it doesn't use the channel in any channel-ish way, you could simply pass len(ch) and cap(ch) directly as the arguments. If you don't like it for any reason, you can play with reflect package, which will allow you to call len and cap on any type supporting it (array, channel, slice).

This might be a good start:

package main

import (
    "fmt"
    "reflect"
)

func stats(i interface{}) {
    v := reflect.ValueOf(i)
    fmt.Printf("%s size: %d/%d\n", v.Kind(), v.Len(), v.Cap())
}

func main() {
    ch := make(chan int, 10)
    ch <- 1
    stats(ch)
}

// Output: chan size: 1/10

http://play.golang.org/p/2ehYvEmDkS

Upvotes: 1

Volker
Volker

Reputation: 42431

Rephrased a bit:

"Is there a way to cast a directed channel to an undirected?" No there isn't.

"Is there a notion of 'arbitrary channel' (without element type) in Go?" No there isn't. Go has no generics.

You'll have to write several functions.

Upvotes: 1

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