How can I initialize an array in Go without using a for loop?

Initializing an Array in Go Without a For Loop

When working with arrays in Go, it is often necessary to initialize their values. The most straightforward method is to use a for loop, as seen in the following example:

<code class="go">for i := 0; i < n; i++ {
    A[i] = true
}</code>

However, this approach can become tedious for large arrays. Fortunately, there are several alternatives available.

Composite Literals

Composite literals allow you to create and initialize arrays and slices in a more concise manner:

<code class="go">b1 := []bool{true, true, true}
b2 := [3]bool{true, true, true}</code>

Note that composite literals will always initialize the array to the zero value for the given type. In the case of bool, this means all values will be false.

Using a Constant

If you want to initialize all elements to a specific value (e.g., true), you can introduce a constant and use it in the composite literal:

<code class="go">const T = true
b3 := []bool{T, T, T}</code>

Alternative Logic

In certain situations, it can be more efficient to store the inverse of the desired values in the array. This allows you to take advantage of the default zeroed array behavior:

<code class="go">presents := []bool{true, true, true, true, true, true}

// Equivalent to:
missings := make([]bool, 6) // All false (not missing)</code>

Efficient "memset" Operation

If performance is critical, you can consider using the following implementation of the memset operation:

<code class="go">import (
    "bytes"
    "unsafe"
)

func memset(p []interface{}, v interface{}) {
    b := bytes.NewBuffer(make([]byte, unsafe.Sizeof(v)))
    b.Reset()
    for i := range p {
        b.Write(b.Bytes())
        copy(p[i:i+1], *(*[]byte)(unsafe.Pointer(&v)))
    }
}</code>

This approach is particularly efficient for large arrays.

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