How Do I Determine the Size and Number of Initialized Elements in a Go Array?

Determining Array Size in Go

In Go, arrays have fixed sizes, meaning they cannot be resized after creation. Therefore, the length of an array is an intrinsic property of its type. The len() function can reveal this length, which remains constant throughout the array's lifetime.

Counterintuitive len() Behavior

The example provided illustrates a common misunderstanding. The len() function returns the declared size of the array, which is 100 in this case. However, the output might be misleading if you expect it to represent the number of elements initialized to non-zero values.

Uninitialized Arrays in Go

Go arrays are automatically initialized with zero values for all elements. So, even though the array has a declared size of 100, it contains only zeroes until explicit values are assigned to specific indices. This means that the "total items in array" is effectively always the same as the declared size.

Slices: A Different Story

Slices, in contrast to arrays, provide a dynamic view into a portion of an underlying array. They have a length and a capacity, where the capacity is the maximum length to which the slice can be extended. When a slice is extended beyond its current length, Go automatically allocates a larger underlying array and adjusts the slice descriptor accordingly.

If you are interested in the number of non-zero elements within an array, consider using for-range loops to iterate through the elements and count those that are non-zero. Alternatively, you could use slices and modify the slice length as needed.

For a comprehensive understanding of arrays and slices in Go, refer to the recommended blog posts on Go Slices and Arrays. These resources provide detailed insights into the nuances and internal workings of array and slice operations in the Go language.

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