为什么通道类型中带有“ <-”？

Question

This works.

var tick <-chan time.Time = time.Tick(1e8)

However, this does not.

var tick chan time.Time = time.Tick(1e8)

Why do I need a <- in my type declaration for a channel? I thought that <- was for writing to or reading from a channel. Why would it appear in a type?

Answer 1

Channels can have a type indicating whether it is readonly, writeonly or both.

Indicating a channel direction is done with <- as part of the type or omitted for a read/write channel.

So the <- in <-chan time.Time is part of the type,

chan   time.Time  //Would be a read/writable channel
chan<- time.Time  // Would be a write only channel
<-chan time.Time  // Would be a read only channel

and time.Tick(1e8) returns a read only channel.

Read more in the language spec here