How to Avoid the 'assignment to entry in nil map' Error When Creating Slices of Maps in Go?

Assignment to Entry in Nil Map Error: Creating Slices of Maps

When attempting to create slices of maps, it's important to understand how memory in Go is allocated and accessed. The runtime error "assignment to entry in nil map" occurs when trying to assign a value to a nil map entry.

In the provided code, the goal is to create a slice of maps with each map containing two indices: "Id" and "Investor." The initial approach involved making an array of maps:

invs := make([]map[string]string, length)

However, this resulted in a panic error because the invs slice initially contains nil maps. To fix this, the correct declaration is:

a := make([]map[string]int, 100)

which initializes each element of the slice with an empty map.

Next, the code iterates through the maps and populates them with data:

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

This approach creates maps for each entry in the slice. However, a more concise way to populate the maps is using composite literals:

invs[i] = map[string]string{"Id": inv_ids[i], "Investor": inv_names[i]}

which creates an already populated map.

For a more idiomatic approach, consider using structs to represent investors:

type Investor struct {
    Id   int
    Name string
}

and then creating a slice of investors:

a := make([]Investor, 100)
for i := 0; i < 100; i++ {
    a[i] = Investor{Id: i, Name: "John" + strconv.Itoa(i)}
}

This approach provides a cleaner and more type-safe way to represent investor data.

The above is the detailed content of How to Avoid the 'assignment to entry in nil map' Error When Creating Slices of Maps in Go?. For more information, please follow other related articles on the PHP Chinese website!