Go Pass Func to Struct like fields, Error "too few values in struct literal of type Test"

Question

type Test struct {
    a int
    b int
}

func f(a, b int) (int, int) {
    return a, b
}

k := Test{(f(5, 6))} // Error

---

but

type Test struct {
    a int
}

func f(a int) int {
    return a
}

k := Test{(f(5))} // Ok

How send func result to struct fields, or create method for group of types, example:

 func(MyType1, MyType2) f (something) something {}

Answer 1

Even though your function in the first example returns two values, the language specification does not provide a mechanism to distribute multiple return values to implicit fields automatically; you must be explicit.

The simplest way to do this in your first example would be:

   t := Test{}
   t.a, t.b = f(a, b)

Your second question is not entirely clear.

You could mean something similar to:

   func(values ...int) func(...int) []int

i.e. a function accepting a variable number of int arguments, returning a function that also accepts a variable number of int arguments and returns a slice of int.

There is no way to return a variable number of values, other than as a slice.

If the arguments are required to be of (potentially) different types, then you would need to use the any type:

   func(values ...any) func(...any) []any

If you had a specific case where you want two distinct, explicit types in the initial function, then you must be specific about the number and order of those values; when it comes to the return value of the returned function you would again need to resort to any:

   func(v1 int, v1 string) func(int, string) []any

A generic function which could accept two values of any type, where those types are to be specified at the call site, is just a generic [sic] form of the previous case:

   func[T1 any, T2 any](v1 T1, v2 T2) func(T1, T2) []any

Similarly, a generic function could be used for the initial example of 0..n values of a given type:

   func[T any](values ...T) func(...T) []T

Note that the any constraint on the types in these generics may not be appropriate in your specific use case. There is insufficient information to suggest a more appropriate constraint.

I hope that answers your question. If not, you'll need to provide more information about what you are trying to achieve.