Initialize array of arrays with different sizes in Golang

In Golang, I want to initialize an array of arrays which can represent an year.
The main array will have 12 sub-arrays each will represent a month. Each subarray will have size of the month they represent.

For eg, 0th sub-array will reference January and will contain 31 elements, 1st sub-array will reference February and will contain 29 elements (considering a leap year) and so on...

Multi-dimensional arrays are initialized like [12][30]int in Golang considering the fixed size. But here, I am working with a multidimensional array of different sizes. How do I initialize a variable with such a datatype?

In short, I want to do something like this:

var year [[31]int, [29]int, [31]int, [30]int, [31]int, [30]int, [31]int, [31]int, [30]int, [31]int, [30]int, [31]int]

But I am struggling with the syntax. Could someone please help me out? Thanks!!

You want something like this?

package main

import "fmt"

func main() {
	days := []int{31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
	months := [12][]int{}
	for i := 0; i < 12; i++ {
		months[i] = make([]int, days[i])
		fmt.Println(i, months[i], len(months[i]))
	}
}

run in go playground

A slightly more consistent answer reference @Sakib. And I assumed you wanted the dates to be filled too.

days := []int{31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
months := make([][]int, len(days))
for i := 0; i < 12; i++ {
	months[i] = make([]int, days[i])
	for j := 0; j < days[i]; j++ {
		months[i][j] = j + 1
	}
	fmt.Println(i+1, months[i])
}

if you want to initialize an array of arrays which can represent an year and multi-dimensional arrays are initialized like [12][30]int, I think this code may solve your problem:

package main

import (
	"errors"
	"fmt"
	"log"
	"strconv"
	"time"
)

func main() {
	years := []int{
		2022,
		1972,
		2021,
		2020,
	}

	var s string
	for _, year := range years {
		s = ""
		ret, err := GetYearDays(year)
		if err != nil {
			log.Fatal(err)
		}
		for i := range ret {
			s = s + " " + strconv.Itoa(len(ret[i]))
		}
		log.Printf("year: %d, month days:%s\n", year, s)
	}
}

func GetYearDays(year int) (ret [12][]int, err error) {
	// year check depends on the user
	if year < 1952 || year > 3000 {
		return ret, errors.New("invalid year")
	}

	for idx := range ret {
		firstDay, err := time.Parse("2006-1-2", fmt.Sprintf("%d-%d-1", year, idx+1))
		if err != nil {
			return ret, fmt.Errorf("time invalid, year: %d, month: %d", year, idx+1)
		}
		lastDay := firstDay.AddDate(0, 1, -1)
		ret[idx] = make([]int, lastDay.Day())
	}
	return ret, err
}