How can you write to the beginning of a bytes.Buffer in Golang?

Overwriting the Beginning of a Buffer in Golang

In Golang, the bytes.Buffer type can be used to write and read data in a buffer. By default, appending to the buffer is achieved using the WriteString method. However, there may be scenarios where writing to the beginning of the buffer is desired.

Can we write to the beginning of a buffer?

By default, the WriteString method appends the provided string to the end of the buffer. The underlying implementation of bytes.Buffer is not exported, making it difficult to directly access the buffer's underlying slice and modify it.

Solution:

To write to the beginning of a buffer, you can use the following workaround:

1. Append the desired string to the end of the buffer.
2. Retrieve the entire string from the buffer using the String method.
3. Reset the buffer to clear its contents.
4. Write the concatenated string (new string followed by the old string) to the reset buffer.

Example:

<code class="go">package main

import (
    "bytes"
    "fmt"
)

func main() {
    var buffer bytes.Buffer
    buffer.WriteString("B")
    s := buffer.String()
    buffer.Reset()
    buffer.WriteString("A")
    buffer.WriteString(s)
    fmt.Println(buffer.String())
}</code>

Output:

AB

By concatenating and rewriting the string, the code effectively overwrites the contents of the buffer, placing the desired string at the beginning.

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