Cannot use "a" (type string) as type in array element in go

Question

I'm pretty new to Golang and I have an issue with adding items to Array.

I use this link as a reference golang-book.

I have this struct:

package models

type FileMD struct {
    fileName string
    fileSize int
}

I tried to do it both ways but I failed.

fileList := [...]models.FileMD{"a", 1: "b", 2}
var fileList [...]models.FileMD
fileList[0] = "a", 1

What is the correct way?

Answer 1

I am not sure but I think you are looking for:

fileList[0] = FileMD{"a", 1}

Or maybe:

fileList := []FileMD{{"a", 1}, {"b", 2}}

Answer 2

First you need to decide if you want an array or a slice.

Once you decided, you have basically 2 options:

(Try the complete application on the Go Playground.)

1) With a literal:

Initialize your array/slice with a Composite literal (either an array or slice literal) and you're done.

Arrays:

fileArr10 := [2]FileMD{FileMD{"first", 1}, FileMD{"second", 2}}
// Or short:
fileArr11 := [2]FileMD{{"first", 1}, {"second", 2}}
// With length auto-computed:
fileArr20 := [...]FileMD{FileMD{"first", 1}, FileMD{"second", 2}}
// Or short:
fileArr21 := [...]FileMD{{"first", 1}, {"second", 2}}

Slices (note the only difference between array and slice literals is that length is not specified):

fileSl10 := []FileMD{FileMD{"first", 1}, FileMD{"second", 2}}
// Or short:
fileSl11 := []FileMD{{"first", 1}, {"second", 2}}

2) New, initialized array/slice and filling it:

Create a new, initialized array/slice and fill it by assiging values to its elements.

Array:

fileArr := [2]FileMD{}
fileArr[0] = FileMD{"first", 1}
fileArr[1] = FileMD{"second", 2}

Slice: (you can create slices with the built-in function make)

fileSl := make([]FileMD, 2)
fileSl[0] = FileMD{"first", 1}
fileSl[1] = FileMD{"second", 2}

Final Note

Your struct FileMD is part of a package and it contains unexported fields (fields whose name start with lowercased letters).

Unexported fields are not accessible from outside of the package. This also means that when you create a value of such struct, you cannot specify the initial values of unexported fields.

So if you try to create a value of FileMD from outside of package models, you can only create zero-valued FileMDs like this: FileMD{}. Make your fields exported and then you can specify the initial values for the file name and size:

type FileMD struct {
    FileName string
    FileSize int
}

// Now FileMD{"first", 1} is valid outside of package models