If you are a Gopher, you probably heard some advice that goes like this: when you edit a value then use a pointer receiver, when you read use a value receiver. That’s not always correct and you should be careful when using them. Issue Today I encountered an issue which can be simplified by the bellow code snippet: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 package main import ( "fmt" "time" ) type Counter struct { Count int } // Method with pointer receiver func (c *Counter) Increment() { go func() { for i := 0; i < 10; i++ { c.Count++ time.Sleep(1 * time.Second) } }() } // Method with value receiver func (c Counter) Display() { go func() { for i := 0; i < 10; i++ { fmt.Println("counter value: ", c.Count) time.Sleep(1 * time.Second) } }() } func main() { c := Counter{Count: 0} c.Display() c.Increment() time.Sleep(15 * time.Second) fmt.Println("counter final value: ", c.Count) } I have a struct with two methods, Increment uses the pointer receiver to change the property of the struct, and Display uses the value receiver to read the value from the struct. Here is the result: ...

You may have heard about 0.1 + 0.2 != 0.3 already, it’s a common issue in most programming languages. The reason behind that is the floating point (IEEE 754) as the computer can’t represent exactly a decimal in binary. By utilizing the floating point, the computer can hold a very large decimal, but the trade-off is it now can only represent the approximate of the true value. However, in this post, I will not explain how floating point works but something else – constant. ...

this article assumes you have some basic knowledge about Rust smart pointers. the dereference (*) operator dereference operator * is used for getting the actual value from a reference: 1 2 3 let a: i32 = 5; let b: &i32 = &a; assert_eq!(*b, 5); in the above example, b is a reference to a, *b will return the value that b pointing to. the smart pointers Box<T> here is an example of how you can init and modify the value of a Box<T>: ...

a linked list If we use two pointers slow and fast, the first one moves forward one step at a time, and the second one moves forward two steps at a time. Eventually, the two pointers will meet somewhere. In the above example, they meet at number 9 (or G). G is where two-pointers fast and slow meet. E is the entrance of the loop. S is the first node of the linked list. F is the distance from the chain’s beginning to the loop’s entrance (from S to E). (eg: 1 – 3 – 5) a is the distance from the loop’s entrance to the point where two pointers meet (from E to G). (eg: 5 – 6 – 7 – 8 – 9) C is the length of the loop. (eg: the loop is 5 – 6 – 7 – 8 – 9 – 10, the length is 6 ) The total distance that the slow pointer has moved is $F + a + xC$. $x$ is the number of times the slow pointer completes the loop. The total distance that the fast pointer has moved is $F + a + yC$. Likewise, $y$ is the number of times the fast pointer completes the loop. ...

1. Definition set is a collection of unique elements. the word disjoin means non-overlapping – two sets are considered as disjoining if they have no element in common disjoin-set contains a collection of non-overlapping sets it has two method find(x): return the representative element of the set that contains of x if u and v are in the same set, find(u) = find(v) union(u, v): merge two sets that contain u and v after merging, find(v) = find(u) 2. Implementations View the visualization of the data structure here. ...

Explain Explaining the query will help you to estimate how expensive your query is and which query plan will be used. 1 2 3 4 5 6 khanh=# explain select g from grades where g = 100; QUERY PLAN ------------------------------------------------------------------------------- Index Only Scan using g_index on grades (cost=0.42..97.55 rows=4636 width=4) Index Cond: (g = 100) (2 rows) So, this query will use Index-Only-Scan. The cost of the query is ranging from 0.42 to 97.55, 4636 is number of estimated return rows, width is size of return data in byte. ...

Check timezone of the current session 1 2 3 4 5 khanh=# show timezone; TimeZone ---------- UTC (1 row) Change timezone of a session 1 2 3 4 5 6 7 khanh=# set timezone='asia/ho_chi_minh'; SET khanh=# show timezone; TimeZone ------------------ Asia/Ho_Chi_Minh (1 row) you can get timezone names here: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones timestamp and timestamptz timestamptz aka timestamp with time zone, the time when return to the client will be converted to the timezone has picked in the session. ...

What is SSL? and why do we need them? SSL is a method to encrypt your data before transmitting it to the receiver. If we don’t encrypt and send data as plain text, somebody can sniff in your connection to read all your messages. How do SSL works? Of course, to establish an SSL, we need a TCP connection first, let’s assume that we have a TCP connection ready. How an SSL connection is established ...

No! Not really! NodeJS has one main thread called event-loop and it also has a worker pool to handle blocking IO and CPU-intensive tasks. The default number of threads in the worker pool is 4, and you can change it. Node.js uses a small number of threads to handle many clients. In Node.js there are two types of threads: one Event Loop (aka the main loop, main thread, event thread, etc.), and a pool of k Workers in a Worker Pool (aka the threadpool). ...

To demonstrate what is the difference between object hash code and object equal, I would like to start with a simple example in Python. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 class Person: def __init__(self, name: str, age: int) -> None: self.name = name self.age = age def __repr__(self) -> str: return f'{self.name} {self.age}' john = Person('John', 18) eventRegister = {} # John want to join the event eventRegister[john] = True # In the next day, # he changes his mind john = Person('John', 18) eventRegister[john] = False print(f'registers: {eventRegister}') # Check john = Person('John', 18) print(f'Will John join the event? {eventRegister[john]}') It’s quite simple, right? I define a new Person class that has two properties age and name. And then I defined a map, to check if a person join the event or not. ...