dictionary - Deleting pointer value doesn't panic -


why doesn't following code panic? test pointer. fmt.println(people[0].name) instead of fmt.println(test.name) panic. 

package main  import "fmt"  func main() {      type person struct {         id   int         name string     }      people := make(map[int]*person)      people[1] = &person{0, "name"}     fmt.println(people[0].name)      test := people[0]     test.name = "name2"     fmt.println(test.name)      people[0].name = "name3"     fmt.println(test.name)      delete(people, 0)      fmt.println(test.name) }

playground

the use of builtin delete() removes entry map. not delete / deallocate memory pointed value associated removed key.

in go can't manage memory this, go garbage collected language , freeing memory duty , responsibility of garbage collector.

your code doesn't panic because have (valid) pointer value of type person, , long have it, person not become invalid (its memory not freed).

when change code people[0].name, indexing map key not in map (because removed delete()), result of index expression zero value of value type of map, nil *person type. , attempting refer name field of nil struct pointer cause runtime panic.


Comments

Post a Comment

Popular posts from this blog

PHP and MySQL WP -

i trying accomplish 2 things here code. writing php directly wp page using insert php plugin. 1) query mysql database , return results 1 column 4 columns. 2) make each result own hyperlink directs user new wp page runs new query on page. i able query show results , turn results dynamic hyperlink, cannot formatting down. right returns result 1 column. here have: [insert_php] $servername = "localhost"; $username = "login"; //edited privacy $password = "password"; //edited privacy $database = "database"; //edited privacy // create connection $conn = new mysqli($servername, $username, $password, $database); // check connection if ($conn->connect_error) { die("connection failed: " . $conn->connect_error); } echo "connected successfully"; //get results database $result = mysqli_query($conn,"select mine mines order mine"); $all_property = array(); //declare array saving property //showing proper...
Read more

android - InAppBilling registering BroadcastReceiver in AndroidManifest -

i'm implementing inapp billing in android app. works well, however, i'm trying decouple broadcast receiver activity manifest. suggestion in android's trivialdrive sample: // important: dynamically register broadcast messages updated purchases. // register receiver here instead of <receiver> in manifest // because call getpurchases() @ startup, therefore can ignore // broadcasts sent while app isn't running. // note: registering listener in activity bad idea, done here // because sample. regardless, receiver must registered after // iabhelper setup, before first call getpurchases(). currently there's class extends broadcastreceiver : public class iabbroadcastreceiver extends broadcastreceiver { /** * intent action receiver should filter for. */ public static final string action = "com.android.vending.billing.purchases_updated"; private final iabbroadcastlistener mlistener; public iabbroadcastreceiver(iabbroadcastlistener listener) { m...
Read more

nginx - phpPgAdmin - log in works but I have to login again after clicking on any links -

i have setup postgres 9.6 , phppgadmin on centos 7 server nginx, i can log in phppgadmin, postgresql server on right of page remains crossed out , link try browse (databases, roles etc) requires log in again. i'm thinking seems sessions problem, unsure how resolve it. any pointers on how fix or should looking @ in order track down problem? solved. turns out owner of /var/lib/php/session apache - needed nginx. sorted changing ownership nginx below: chown -r nginx:nginx /var/lib/php/session/
Read more