Golang Note Three

Methods

• Go does not have classes. However, you can define methods on struct types.
• The method receiver appears in its own argument list between the func keyword and the method name.
• You can declare a method on any type that is declared in your package, not just struct types.
• You cannot define a method on a type from another package (including built in types).
• Methods can be associated with a named type or a pointer to a named type.
  • There are two reasons to use a pointer receiver.
  • Avoid copying the value on each method call (more efficient if the value type is a large struct)
  • The method can modify the value that its receiver points to.

Interfaces

• An interface type is defined by a set of methods.
• A value of interface type can hold any value that implements those methods.
• One of the most ubiquitous interfaces is Stringer defined by the fmt package.
• A Stringer is a type that can describe itself as a string.

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type Stringer interface {
    String() string
}

Errors

• Go programs express error state with error values.
• The error type is a built-in interface simliar to fmt.Stringer

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type error interface {
    Error() string
}

• Functions often return an error value, and calling code should handle errors by testing whether the error equals nil.

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i, err := strconv.Atoi("42")
if err != nil {
    fmt.Printf("couldn't convert number: %v\n", err)
}
fmt.Println("Converted integer:", i)

Readers

• The io package specifies the io.Reader interface, which represents the read end of a stream of data.

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func (T) Read(b []byte) (n int, err error)

Read populates the given byte slice with data and returns the number of bytes populated and an error value. It returns an io.EOF error when the stream ends.

Web servers

• Package http serves HTTP requests using any value that implements http.Handler

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package http

type Handler interface {
    ServeHTTP(w ResponseWriter, r *Request)
}