How to Efficiently Convert CGO Arrays to Go Slices: Safe vs. Unsafe Methods?

Unconventional Casting: Converting CGO Arrays to Go Slices

When working with CGO in Go, one may encounter the need to cast a CGO array into a Go slice. Traditionally, this involves a manual conversion by iterating over the array and casting each element individually.

However, there exist more efficient and unconventional approaches to this task.

Safe and Straightforward Method:

The safer and more recommended approach is to use a for loop to manually cast each element of the CGO array:

c := [6]C.double{1, 2, 3, 4, 5, 6}
fs := make([]float64, len(c))
for i := range c {
    fs[i] = float64(c[i])
}

This method guarantees type safety and portability.

Unconventional but Efficient Method:

For speed and efficiency, a more daring approach can be employed, known unsafe type casting:

c := [6]C.double{1, 2, 3, 4, 5, 6}
cfa := (*[6]float64)(unsafe.Pointer(&c))
cfs := cfa[:]

This technique relies on the assumption that C.double and float64 share the same underlying type. It involves taking a pointer to the CGO array, casting it unsafely to a pointer to a float64 array of the same size, and finally taking a slice of that array.

Caveats and Considerations:

While the unsafe conversion method may be faster, it comes with the caveat of potential undefined behavior and platform-dependency. It is important to ensure that the underlying types of C.double and float64 are indeed compatible before employing this approach. Additionally, it is critical to use this technique only when necessary and with utmost caution.

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