Blog / Go Language Spec

Channel types

May 16, 2023

Channel types

A channel provides a mechanism for concurrently executing functions to communicate by sending and receiving values of a specified element type. The value of an uninitialized channel is nil.

ChannelType = ( "chan" | "chan" "<-" | "<-" "chan" ) ElementType .

Channels are one of the most confusing parts of Go, for many newcomers. But they don’t need to be. They’re actually quite simple.

Think of a channel as an array, which can only be read from one end, and appended to the other.

There are a few other rules around how channels work, which we’ll of course get to, but from a data type standpoint, that serves as a useful summary.

There are no magical scoping or garbage collection rules. Channels don’t do anything. They’re just a data type. They just hold data, and they go out of scope, get garbage collected, can be passed around, assigned, re-assigned, just as any other type can.

Quotes from The Go Programming Language Specification Version of December 15, 2022

Share this

Related Content

Directional channels

Channel types … The optional <- operator specifies the channel direction, send or receive. If a direction is given, the channel is directional, otherwise it is bidirectional. A channel may be constrained only to send or only to receive by assignment or explicit conversion. chan T // can be used to send and receive values of type T chan<- float64 // can only be used to send float64s <-chan int // can only be used to receive ints When you create a new channel, you get a bidirectional channel.

Type identities of other types

Type identity … Two pointer types are identical if they have identical base types. Given: type ( P = *int Q = P R *int ) P, Q, and *int are all identical to each other, but different from *int32 and R. Two function types are identical if they have the same number of parameters and result values, corresponding parameter and result types are identical, and either both functions are variadic or neither is.

Channel synchronization

I’ve made the case that channels are just data types, and non-magical. So why should we care about channels, rather than just using some sort of slice, array, or custom first-in-first-out queue? The reason is that channels provide us certain guarantees with regard to synchronization. The spec explains: Channel types … A single channel may be used in send statements, receive operations, and calls to the built-in functions cap and len by any number of goroutines without further synchronization.