How to Efficiently Create Deep Copies of Maps in Go?

Making Copies of Maps in Go: Is There a Built-In Function?

Maps in Go are a versatile data structure, but the lack of a built-in function for creating copies can be a hurdle. Fortunately, several approaches can help you achieve this.

Using the encoding/gob Package

For a general solution, the encoding/gob package provides a robust way to make deep copies of complex data structures, including maps. By encoding the original map and then decoding it into a new variable, you create a copy that references a different memory location.

package main

import (
    "bytes"
    "encoding/gob"
    "fmt"
    "log"
)

func main() {
    ori := map[string]int{
        "key":  3,
        "clef": 5,
    }

    var mod bytes.Buffer
    enc := gob.NewEncoder(&mod)
    dec := gob.NewDecoder(&mod)

    fmt.Println("ori:", ori) // key:3 clef:5
    err := enc.Encode(ori)
    if err != nil {
        log.Fatal("encode error:", err)
    }

    var cpy map[string]int
    err = dec.Decode(&cpy)
    if err != nil {
        log.Fatal("decode error:", err)
    }

    fmt.Println("cpy:", cpy) // key:3 clef:5
    cpy["key"] = 2
    fmt.Println("cpy:", cpy) // key:2 clef:5
    fmt.Println("ori:", ori) // key:3 clef:5
}

By using encoding/gob, you can create deep copies that respect even nested structures, like slices of maps or maps containing slices.

Other Considerations

While encoding/gob offers a general solution, it may not be suitable for all cases. If your maps are relatively simple, you may consider writing a custom function for creating shallow copies. Additionally, there are third-party libraries that provide map copying functionality.

Remember that copies in Go are always deep, meaning they create new instances of the data, unlike shallow copies, which only create references to the original. This is an important distinction to consider when manipulating maps.

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