How to Use Arrays as Parameters in Golang?

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Declaring Arrays in Golang
Passing Arrays as Function Parameters
Using Slices as Function Parameters
Practical Example: Paginating Data
Conclusion

In Golang, arrays are a fundamental data structure that can be passed as parameters to functions. This article will explain how to use arrays as parameters in Go, including examples of passing arrays with fixed sizes and using slices for more flexibility.

1. Declaring Arrays in Golang

Before passing arrays as parameters, let's review how to declare arrays in Go.

package main

import "fmt"

func main() {
    // Declare an array with a fixed size of 5
    var numbers [5]int
    fmt.Println(numbers) // Output: [0 0 0 0 0]

    // Declare an array with initial values
    primes := [5]int{2, 3, 5, 7, 11}
    fmt.Println(primes) // Output: [2 3 5 7 11]
}

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2. Passing Arrays as Function Parameters

To pass an array as a parameter to a function, you need to declare the function parameter as an array with a fixed length. Here’s an example:

package main

import "fmt"

// Function that accepts an array with a fixed length of 5
func printArray(arr [5]int) {
    for i, value := range arr {
        fmt.Printf("Element %d: %d\n", i, value)
    }
}

func main() {
    primes := [5]int{2, 3, 5, 7, 11}
    printArray(primes)
}

In the above example, the printArray function accepts a parameter of type array with a length of 5 elements.

3. Using Slices as Function Parameters

In Go, it’s more common to use slices than arrays when passing a collection of data to a function. Slices are more flexible because they do not have a fixed length like arrays.

package main

import "fmt"

// Function that accepts a slice
func printSlice(slice []int) {
    for i, value := range slice {
        fmt.Printf("Element %d: %d\n", i, value)
    }
}

func main() {
    primes := []int{2, 3, 5, 7, 11}
    printSlice(primes)
}

In the example above, the printSlice function accepts a parameter of type slice. You can change the length of a slice without needing to redeclare it like an array.

4. Practical Example: Paginating Data

Let’s apply this concept in a practical example. Suppose you want to create a function to paginate data from a database using GORM in Go. Here is a simple implementation:

package main

import (
    "github.com/gin-gonic/gin"
    "gorm.io/driver/sqlite"
    "gorm.io/gorm"
    "net/http"
    "reflect"
    "strconv"
)

type Product struct {
    ID   int    `json:"id"`
    Name string `json:"name"`
}

func main() {
    r := gin.Default()

    db, _ := gorm.Open(sqlite.Open("test.db"), &gorm.Config{})
    db.AutoMigrate(&Product{})

    r.GET("/products", func(ctx *gin.Context) {
        var responseDto []Product

        page, _ := strconv.Atoi(ctx.DefaultQuery("page", "1"))
        perPage, _ := strconv.Atoi(ctx.DefaultQuery("per_page", "10"))

        ResponseWithPaginate(db, &Product{}, &responseDto, ctx, page, perPage)
    })

    r.Run()
}

func ResponseWithPaginate(c *gorm.DB, data interface{}, responseDto interface{}, ctx *gin.Context, page int, perPage int) {
    var totalItems int64

    err := c.Model(data).Count(&totalItems).Error
    if err != nil {
        ctx.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
        return
    }

    result := c.Limit(perPage).Offset((page - 1) * perPage).Find(responseDto)
    if result.Error != nil {
        ctx.JSON(http.StatusNotFound, gin.H{"error": result.Error.Error()})
        return
    }

    meta := NewMeta(ctx, totalItems, int64(reflect.ValueOf(responseDto).Elem().Len()))

    SuccessResponse(ctx, responseDto, meta)
}

func NewMeta(ctx *gin.Context, totalItems, itemCount int64) map[string]interface{} {
    return map[string]interface{}{
        "total_items": totalItems,
        "item_count":  itemCount,
    }
}

func SuccessResponse(ctx *gin.Context, data interface{}, meta map[string]interface{}) {
    ctx.JSON(http.StatusOK, gin.H{
        "data": data,
        "meta": meta,
    })
}

In the example above, the ResponseWithPaginate function accepts a slice as a parameter for responseDto. This slice is used to store the results of the query from the database.

Conclusion

Using arrays or slices as parameters in functions in Golang is straightforward and intuitive. Slices are often preferred due to their flexibility in size. By understanding these basics, you can easily manage and manipulate collections of data in your Go programs.

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