How to Efficiently Cast CGO Arrays to Go Slices?

Casting CGO Arrays into Go Slices: A Comprehensive Guide

In Go, casting between CGO arrays and slices can be a common task, but it can also be a bit cumbersome. Let's explore the different ways to achieve this conversion efficiently.

Safe and Explicit Method

The standard and most straightforward approach is to use a loop to manually convert each element of the CGO array into a corresponding element of the Go slice. Here's an example:

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 is reliable and ensures type safety, but it can be verbose and time-consuming for large arrays.

Unsafe but Efficient Method

If performance is a primary concern, you can opt for a more direct but inherently unsafe approach. This involves using pointer arithmetic and unsafe casting:

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

Here, a pointer to the CGO array is unsafely cast to a pointer to a corresponding float64 array, and a slice of that array is created. This approach assumes that C.double and float64 have the same underlying type, which may not always be the case. It's essential to exercise caution when using this method.

Which Method to Choose?

The choice between the safe and unsafe methods depends on the specific requirements of your application. If accuracy and type safety are paramount, the safe method is recommended. However, if performance is critical and you can ensure type compatibility, the unsafe method may be a suitable option.

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