Append returns the updated slice. It is therefore necessary to store the result of append, often in the variable holding the slice itself.
Example: var posts []Post posts = append(posts, newItem)
Vars(r)
Vars is a function provided by the gorilla/mux package. It extracts the route variables (e.g posts/id: posts and id are route variables) from the request. These variables are the dynamic segments of the URL defined in the route pattern
mux.Vars(r)
This function call extracts the route variables from the HTTP request r and returns them as a map[string]string. In this map, the keys are the names of the variables defined in the route pattern, and the values are the corresponding values extracted from the URL.
[]byte("ID could not be converted to integer")
[]byte is a type conversion that converts the string "ID could not be converted to integer" into a slice of bytes ([]byte). In Go, a string is essentially a read-only slice of bytes, but to write it using the Write method, it needs to be explicitly converted to a []byte.
Detailed Explanation
- Conversion to Byte Slice:
The string "ID could not be converted to integer" is converted to a byte slice using []byte(). This is necessary because the Write method of http.ResponseWriter accepts a byte slice as its argument. In Go, this conversion changes the data type but retains the content of the string as a sequence of bytes.
- Writing to the Response Body:
The Write method is then called on the http.ResponseWriter object w, with the byte slice as its argument. This method writes the given data to the HTTP response body. In the context of an HTTP server, this means the message "ID could not be converted to integer" will be sent back to the client as part of the HTTP response body.
The Write method typically belongs to types that implement the io.Writer interface. The io.Writer interface is defined as:
type Writer interface { Write(p []byte) (n int, err error) }
So, the function writes the byte representation of the string "ID could not be converted to integer" to the writer w. The Write method returns the number of bytes written and an error if any occurs, though these return values are not captured in the given snippet.
In a practical scenario, w could be any type that implements the io.Writer interface, such as an HTTP response writer (http.ResponseWriter), a file (os.File), or a buffer (bytes.Buffer), among others.