我有2张地图：
map<int,BigObject> a,b;
如果a和b不共享任何密钥，是否有办法将b合并到a，而BigObject不会复制BigObject个对象？
复制function deliver_mail() {
// if the submit button is clicked, send the email
if ( isset( $_POST['cf-submitted'] ) ) {
$errors = array();
if (empty($_POST["cf-name"])){
$nameError = "Name is required";
} else {
$name = sanitize_text_field( $_POST["cf-name"] );
}
// sanitize form values
$name = sanitize_text_field( $_POST["cf-name"] );
$email = sanitize_email( $_POST["cf-email"] );
$phone = "Phone: " . sanitize_text_field( $_POST["cf-phone"] );
$company = "Company: " . sanitize_text_field( $_POST["cf-company"] );
$deliverablesArr = $_POST["formDeliverables"];
$deliverables = implode( $deliverablesArr);
$body = esc_textarea( $_POST["cf-body"] );
$date_from = "None";
if (empty($_POST["date_from"])){
$errors[] = 'Please choose a start date.';
} else {
$date_from = $_POST['date_from'];
}
$date_end = "None";
if (empty($_POST["date_end"])){
$errors[] = 'Please choose an end date.';
} else {
$date_end = $_POST['date_end'];
}
$date_span = $date_from . " - " . $date_end;
$price = $_POST['price'];
$price_two = $_POST['price-two'];
$budget = $price . " - " . $price_two;
$subject = "Someone needs " . $deliverables . " from a-three.cc!";
$copy = 'None';
if(isset($_POST['copy']) && is_array($_POST['copy']) && count($_POST['copy']) > 0){
$copy = implode(', ', $_POST['copy']);
} else {
$errors[] = 'Please choose if copy is needed.';
}
$design = 'None';
if(isset($_POST['design']) && is_array($_POST['design']) && count($_POST['design']) > 0){
$design = implode(', ', $_POST['design']);
} else {
$errors[] = 'Please choose if design is needed.';
}
$illustration = 'None';
if(isset($_POST['illustration']) && is_array($_POST['illustration']) && count($_POST['illustration']) > 0){
$illustration = implode(', ', $_POST['illustration']);
} else {
$errors[] = 'Error: Please choose if Illustration is needed';
}
$photography = 'None';
if(isset($_POST['photography']) && is_array($_POST['photography']) && count($_POST['photography']) > 0){
$photography = implode(', ', $_POST['photography']);
} else {
$errors[] = 'Please choose if Photography is needed.';
}
// get the blog administrator's email address
$to = get_option( 'admin_email' );
$message = '<html><body>';
$message .= '<table rules="all" style="border: 1px solid #666; width: 600px;" cellpadding="10">';
$message .= "<tr style='background: #eee;'><td style='font-size: 16px' colspan='2'><strong><center>Contact from A-Three</center></strong> </td></tr>";
$message .= "<tr><td><strong>Name:</strong> </td><td>" . $name . "</td></tr>";
$message .= "<tr><td><strong>Email:</strong> </td><td>" . $email . "</td></tr>";
$message .= "<tr><td><strong>Company:</strong> </td><td>" . $company . "</td></tr>";
$message .= "<tr><td><strong>Phone:</strong> </td><td>" . $phone . "</td></tr>";
$message .= "<tr><td><strong>Deliverables:</strong> </td><td>" . $deliverables . "</td></tr>";
$message .= "<tr style='background: #eee;'><td style='font-size: 16px' colspan='2'><strong><center>Services Needed</center></strong> </td></tr>";
$message .= "<tr><td><strong>Copy:</strong> </td><td>" . $copy . "</td></tr>";
$message .= "<tr><td><strong>Design:</strong> </td><td>" . $design . "</td></tr>";
$message .= "<tr><td><strong>Illustration:</strong> </td><td>" . $illustration . "</td></tr>";
$message .= "<tr><td><strong>Photography:</strong> </td><td>" . $photography . "</td></tr>";
$message .= "<tr style='background: #eee;'><td style='font-size: 16px' colspan='2'><strong><center>Timeline</center></strong> </td></tr>";
$message .= "<tr><td><strong>Timeline:</strong> </td><td>" . $date_span . "</td></tr>";
$message .= "<tr style='background: #eee;'><td style='font-size: 16px' colspan='2'><strong><center>Budget</center></strong> </td></tr>";
$message .= "<tr><td><strong>Budget:</strong> </td><td>" . $budget . "</td></tr>";
$message .= "<tr style='background: #eee;'><td style='font-size: 16px' colspan='2'><strong><center>Project Description</center></strong> </td></tr>";
$message .= "<tr><td><strong>Project Description:</strong> </td><td>" . $body . "</td></tr>";
$headers = 'From: ' . $email . "\r\n" . 'Reply-To: ' . $email . "\r\n";
$headers .= "MIME-Version: 1.0\r\n";
$headers .= "Content-Type: text/html; charset=ISO-8859-1\r\n";
对象是瓶颈。
答案 0 :(得分：5)
你应该做的第一件事是让BigObject移动成本低廉，并且可以使它成为无副本。一种方法是将他们庞大而昂贵的状态转移到std::unique_ptr< InternalState >。如果您仍然需要副本（我发现您经常不这样做），您可能需要一个value_ptr< InternalState >，要么从boost这样的库中获取值ptr，要么写一下自己的。
如果失败了，你可以等待C ++ 17。在C ++ 17中，（某些？）基于关联节点的容器能够快速移动它们之间的节点集。这包括std::map。
如果失败，您的地图可以从密钥到unique_ptr<BigObject>。这为地图的其他用途添加了少量间接，但它们现在可以便宜地移动。
答案 1 :(得分：0)
正如一些评论指出的那样，如果复制BigObject是昂贵的，那么你应该首先处理指针或引用......
但是如果碰巧只合并了很少的地图，那么你可以编写一个包装器，在读取（和写入......）时按顺序检查几个合并的地图。