Optimizing Performance with Slice Capacity

Snippet

Optimizing Performance with Slice Capacity

When using append, Go may need to reallocate the underlying array if the capacity is exceeded. By providing a capacity hint in make(), you reduce CPU overhead and memory fragmentation.

snippet.go
go
func efficientAppend() {
	// Pre-allocate capacity to avoid multiple reallocations
	data := make([]int, 0, 100)
	for i := 0; i < 100; i++ {
		data = append(data, i)
	}
	fmt.Println(len(data), cap(data))
}

Breakdown

make([]int, 0, 100)

Initializes a slice with length 0 and capacity for 100 elements.

append(data, i)

Adds elements without triggering a new memory allocation until 100 is reached.

cap(data)

Returns the maximum number of elements the slice can hold without reallocating.

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Optimizing Performance with Slice Capacity

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