GoLang Empty Struct Construction-CodePudding

Can someone explain why this

m := map[string]struct{}{"hello": {}}

is valid go code but this

c := make(chan struct{}, 1)
c <- {}

is not? It seems like I'm able to construct the struct via just {} in the first statement but I need to do struct{}{} for the second.

CodePudding user response：

Its not apples to apples. If you try this instead, you get same error:

package main

func main() {
   m := make(map[string]struct{})
   m["hello"] = {} // syntax error: unexpected {, expecting expression
}

As to your greater question, I believe that is answered here [1]:

Within a composite literal of array, slice, or map type T, elements or map keys that are themselves composite literals may elide the respective literal type if it is identical to the element or key type of T.

So for example, if you have a composite literal:

map[string]struct{}

where elements are also composite literal:

struct{}

Then you can omit the type:

{}

https://golang.org/ref/spec#Composite_literals