这行代码在golang中意味着什么？ [重复]

I want to know what does this line of code mean in go,

I am using : "github.com/dgrijalva/jwt-go"

thanks,

   _, ok := token.Method.(*jwt.SigningMethodHMAC)


// for the all the function : 

func TokenValid(r *http.Request) error {
    tokenString := ExtractToken(r)
    token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
        if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
            return nil, fmt.Errorf("Unexpected signing method: %v", token.Header["alg"])
        }
        return []byte(os.Getenv("API_SECRET")), nil
    })
    if err != nil {
        return err
    }
    if claims, ok := token.Claims.(jwt.MapClaims); ok && token.Valid {
        Pretty(claims)
    }
    return nil
}

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