在golang中声明具有任意返回类型的函数类型

Question

I'm new to go and have come across the following issue that I haven't been able to find covered in the tutorial or google searches, though I'm sure it must be a basic aspect of the language I have missed. I have code like the following:

type Task func()

var f Task = func() { fmt.Println("foo") }

type TaskWithValue func() interface{}

var g TaskWithValue = func() { return "foo" }

var h TaskWithValue = func() { return 123 }

In f above, there is no compiler error, but for g and h there are errors like the following:

Cannot use func() { return "foo" } (type func ()) as type TaskWithValue in assignment

Essentially, I'm trying to define a Task type that can have an arbitrary return type. In other languages, I would simply give Task a type parameter, like Task<Integer> or Task<String>, but since go does not have generics/templates, I understood the workaround is to use return type interface{} and then cast the results. What am I missing to get this example working?

Answer 1

You're missing the return type in the anonymous function expressions:

var g TaskWithValue = func() interface{} { return "foo" }

var h TaskWithValue = func() interface{} { return 123 }