Why Can\'t I Directly Convert Between Slices of Different Element Types in Go?

Why You Can't Convert Slice Types

When attempting to convert a slice of one type to another, as in the code segment provided, Go raises an error. This error is due to specific type conversion rules defined in the Go specification.

The error occurs because the underlying type of a slice is not directly related to the underlying type of its elements. While the underlying types of Foo and Bar are identical, the underlying types of slices containing Foo and Bar elements differ.

According to Go's Assignability rules, a value of type []Foo cannot be assigned to a variable of type []Bar. This discrepancy results in the conversion error.

To resolve this issue, the conversion can be done through an intermediate data structure. For instance, the following code works:

<code class="go">type Foo struct{ A int }
type Bars []Foo

func main() {
    foos := []Foo{Foo{1}, Foo{2}}
    bars := Bars(foos)
    fmt.Println(bars)
}
</code>

Output:

[{1} {2}]

Additionally, using the unsafe package can bypass type safety checks and allow for the conversion. However, the unsafe package should be used cautiously and only in exceptional cases where performance and complexity are key concerns.

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