How to Fix "Assignment to Entry in Nil Map" Error When Creating a Slice of Maps in Go?

Runtime Error: "Assignment to Entry in Nil Map" Resolved

When attempting to create a slice of Maps, you may encounter the runtime error "assignment to entry in nil map." This error indicates that you are trying to access a nil Map value, which is not permitted.

Problem Statement

You are experiencing this error while building an array of Maps, each containing two keys: "Id" and "Investor." The attempted code is as follows:

<code class="go">for _, row := range rows {
    invs := make([]map[string]string, length)

    for i := 0; i < length; i++ {
        invs[i] = make(map[string]string)
        invs[i]["Id"] = inv_ids[i]
        invs[i]["Investor"] = inv_names[i]
    }
}</code>

Resolution

To resolve this error, you should create a slice of Maps directly within the loop instead of creating nil Maps and assigning values to them. This can be achieved using composite literals:

<code class="go">for _, row := range rows {
    invs := make([]map[string]string, length)

    for i := 0; i < length; i++ {
        invs[i] = map[string]string{"Id": inv_ids[i], "Investor": inv_names[i]}
    }
}</code>

Alternative Approach

Alternatively, you can use a struct to represent an investor:

<code class="go">type Investor struct {
    Id       int
    Investor string
}

for _, row := range rows {
    invs := make([]Investor, length)

    for i := 0; i < length; i++ {
        invs[i] = Investor{
            Id:       inv_ids[i],
            Investor: inv_names[i],
        }
    }
}</code>

Using a struct provides a cleaner and more structured representation of your data.

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