How to move data from one slice of structs to another?

I have two structs:

type A struct {
    Field1 string
    Field2 int
    Field3 int
}
type B struct {
    Field1 string
    Field2 int
}

I want to convert a slice of []A data(aData) to a slice of []B data (bData).

What is the idiomatic way to do so?

What I tried is this:

var newItem B
var aData []A	
var bData []B


aData = [{"bob", 3, 4}, {"mary", 5, 2}]	


for i:=0 ; i < len(aData); i++ {

	newItem = {aData[i].Field1, aData[i].Field2}
	bData = append( bData, newItem )
}

But it gives:

> syntax error: missing operand

First, your code is invalid. You need a valid array expression for your aData declaration, and you need to specify the type when assigning to bData.

aData := []A{{"bob", 3, 4}, {"mary", 5, 2}}
bData := make([]B, len(aData))

for i, aItem := range aData {
    bData[i] = B{
        Field1: aItem.Field1,
        Field2: aItem.Field2,
    }
}

So aside from your syntax errors, this is more idiomatic because:

1. It uses range instead of a for loop, which is perfect for iterating over an array, and more readable.
2. bData is preallocated to the exact size needed.
3. Field names are specified in the declaration of bData's values. It would be more idiomatic to do the same for aData as well, but it gets a bit verbose.