What is the Maximum Size of a Go Slice and Why Are There Limits?

Maximum Length of a Slice in Go

When creating slices in Go, it's important to consider the limitations posed by the system and the underlying hardware. The article addresses questions regarding the maximum slice size that can be created, exploring the concepts of memory constraints and integer type limitations.

Exploring Slice Size Limitations

The initial code sample demonstrates the creation of a slice containing boolean values, with a size equal to math.MaxInt32. This results in a slice of size 2147483647. However, increasing the slice size to math.MaxUint32 leads to a "fatal error: runtime: out of memory" message.

Error Variations and Underlying Limitations

Attemping to create a slice using math.MaxInt64 results in a "panic: runtime error: makeslice: len out of range" error. This error occurs due to an internal safety check in Go's runtime that ensures the slice size does not exceed the maximum size allowed by the system's memory and integer type limitations. Specifically, the error is triggered when the product of the slice length and the size of each element (in this case, a boolean) exceeds the maximum memory size allowed by the system.

Influence of Element Type

Interestingly, when replacing the boolean elements with struct{} elements, which take no memory, a slice of math.MaxInt64 elements can be created successfully. This highlights that the error message ("not enough memory") can vary depending on the element type used in the slice and the underlying constraints imposed by the system's limitations.

Conclusion

Based on the provided information and the Go documentation, the maximum slice size in Go is determined by the system's memory limitations and the underlying integer type used to index the slice elements. The error messages encountered when exceeding these limitations provide guidance on the nature of the issue and the specific constraints that were violated.

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