What is the Maximum Length of a Slice in Go and What Errors Can Occur When Exceeding It?

Maximum Length of a Slice in Go

In Go, slices are dynamic arrays that can grow and shrink as needed. The length of a slice is the number of elements it contains, while its capacity is the maximum number of elements it can hold without reallocating memory.

Maximum Slice Size

According to the Go documentation, the maximum capacity of a slice is determined by the size of the default integer on the target build. This means that the maximum length of a slice is:

math.MaxUint32 / element size

For a 64-bit Linux OS with 4Gb of memory, the maximum size of a slice is:

math.MaxUint32 / 1 = 4294967295

Out of Memory vs. Len Out of Range Errors

When attempting to create a slice with a size larger than the maximum capacity, you may encounter either an "out of memory" error or a "len out of range" error. The conditions for each error type are as follows:

• "Out of memory" error: This error is raised when the operating system is unable to allocate enough memory for the slice. This can occur when the requested slice size is too large, even if it falls within the theoretical maximum capacity.
• "Len out of range" error: This error is raised when the requested slice size is greater than the maximum capacity based on the size of the default integer on the target build. This error prevents the creation of slices with invalid sizes, even if there is sufficient memory available.

Special Case: Zero-Size Elements

It's important to note that the element size plays a role in the maximum slice size calculation. In the case of a slice of struct{}, which has zero size, the maximum slice length becomes:

math.MaxUint32 / 0 = undefined

Since division by zero is undefined, it's not possible to calculate a meaningful maximum length for a slice of zero-size elements. In such cases, Go allows the creation of slices with extremely large lengths, as seen in the example provided.

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