Why Does `bytes.Buffer` Fail to Implement `io.Writer` in Go, and How Can It Be Fixed?

Implementing io.Writer for String-Writing Objects

In Go, we often need to create objects that implement the io.Writer interface to handle writing operations. However, when attempting to use bytes.Buffer, a confusion can arise despite its implementation of the Write method.

Error Explanation

The error message "bytes.Buffer does not implement io.Writer" occurs because bytes.Buffer has a pointer receiver for its Write method:

func (b *Buffer) Write(p []byte) (n int, err error)

This means that the method must be called on a pointer to the buffer, not on the buffer itself. Attempting to pass the buffer directly, as shown in the code snippet below, causes the error.

var b bytes.Buffer
foo := bufio.NewWriter(b)

Solution: Passing a Pointer to the Buffer

To resolve this error, we need to pass a pointer to the buffer instead of the buffer itself. This is because bufio.NewWriter expects a io.Writer interface, and the pointer to the buffer implements this interface correctly.

var b bytes.Buffer
foo := bufio.NewWriter(&b) // Pass a pointer to the buffer

With this modification, the program will successfully create a writer that writes to the string buffer.

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