为什么在遍历结构片段时无法访问结构字段

I have a function in a package which returns a slice of a specific struct I defined in my package, then I'm importing this package to another main package and I want to iterate over the slice returned from the function and access the structs fields, I'm getting "undefined" error.

"s.a undefined (cannot refer to unexported field or method a)"

What am I missing?

thanks for the help.

the packages code:

package test_package

import "fmt"

type Struct struct {
    a string
    b string
}

func ReturnStructSlice() ([]Struct){
    s1 := Struct{"a", "b"}
    s2 := Struct{"c", "d"}

    structSliceToReturn := []Struct{s1, s2}

    for _, s := range structSliceToReturn {
        fmt.Println(" ", s.a)
    }

    return structSliceToReturn
}

this is the main package:

package main

import (
    t "/test_package"
    "fmt"
)


func main() {
    sList := t.ReturnStructSlice()
    for _, s := range sList {
        fmt.Println(" ", s.a) \\ here I'm getting the error
    }
}

You need to capitalize the first letter of struct members to export them.

type Struct struct {
    A string
    B string
}