I have the following definition:

```
func (c *Collector) RegisterSource(f func() []interface{}) {
    c.source = f
}

```

I attempt to call it as follows but get an error:

```
func source() []int {
    return []int{ 0, 1, 2, 3, 4 }
}
...
c.RegisterSource(source)

```

This is met with:

```
cannot use source (type func() []int) as type func() []interface {} in argument to c.RegisterSource

```