go-cap-learn.go

package main

import (
	"fmt"
	"time"
)

func main() {
	const iterations = 1000000 // Using a large number to make the difference more noticeable

	// Measure time for slice without pre-allocated capacity
	startNoCapacity := time.Now()
	noCapacity := make([]int, 0)
	for i := 0; i < iterations; i++ {
		noCapacity = append(noCapacity, i)
	}
	durationNoCapacity := time.Since(startNoCapacity)

	// Measure time for slice with pre-allocated capacity
	startWithCapacity := time.Now()
	withCapacity := make([]int, 0, iterations)
	for i := 0; i < iterations; i++ {
		withCapacity = append(withCapacity, i)
	}
	durationWithCapacity := time.Since(startWithCapacity)

	// Print results
	fmt.Printf("Without capacity: %v\n", durationNoCapacity)
	fmt.Printf("With capacity:    %v\n", durationWithCapacity)
	fmt.Printf("Performance gain: %.2fx faster\n", float64(durationNoCapacity)/float64(durationWithCapacity))

	// Memory usage demonstration (just the length and capacity at the end)
	fmt.Printf("\nFinal slice stats:\n")
	fmt.Printf("Without capacity: len=%d cap=%d\n", len(noCapacity), cap(noCapacity))
	fmt.Printf("With capacity:    len=%d cap=%d\n", len(withCapacity), cap(withCapacity))
}


// Without capacity: 18.753703ms
// With capacity:    871.065µs
// Performance gain: 21.53x faster

// Final slice stats:
// Without capacity: len=1000000 cap=1055744
// With capacity:    len=1000000 cap=1000000