C#•11mo ago

What is meant by "Generic" and where do we use them and why are they important

Hello guys, sorry to disturb you all; can someone explain what is meant by "generic" please; does this applies only to OOP concept? or any programming language with collections? Like I know the angular brackets is used to define a generic. But why do we need them? What would happen without generics?

FakerOP•1/30/25, 5:29 PM

For example, I'm reading that there are kind of 2 type of hashtable, a non-generic one and a generic one (dictionary)

FakerOP•1/30/25, 5:29 PM

why does it matter pls

Angius•1/30/25, 5:32 PM

It means there's a that can hold key-value pairs

Angius•1/30/25, 5:33 PM

And a that can hold key-value pairs of specified type

Angius•1/30/25, 5:33 PM

To be clear, you should never use the former

Angius•1/30/25, 5:33 PM

Generics are a way to pass a type as a parameter

Angius•1/30/25, 5:33 PM

For example, a can be

List<int>

List<int>

, telling the compiler that it will hold only

int

int

Angius•1/30/25, 5:34 PM

Or you can have a

that will have the of a specified type

Angius•1/30/25, 5:34 PM

will make it so that will be a string

Angius•1/30/25, 5:38 PM

To answer your question about world without generics... there was a time that C# did not have them

Angius•1/30/25, 5:38 PM

That's where and are from

Angius•1/30/25, 5:38 PM

They would hold

object

object

s and pairs

Angius•1/30/25, 5:39 PM

So you would need to cast everything

Angius•1/30/25, 5:39 PM

Instead of doing you would have to do every time

Angius•1/30/25, 5:40 PM

Not to mention performance issues

Angius•1/30/25, 5:40 PM

https://github.com/Atulin/Solution1/tree/master/Collections

Angius•1/30/25, 5:40 PM

I gave a talk during Solution1 that touched upon non-generic collections

Angius•1/30/25, 5:40 PM

In this repo, you can find examples of using both generic and non-generic ones, as well as benchmark results

AlkalineLemon•1/30/25, 5:42 PM

generics let you make classes and methods that use a general type

For example,
if you wanted to make a method to swap two variables of the some time, you could do it in two ways
1- Write out swap methods separately for int, float, double, string, etc, etc
2- Use generics to make one method that can accept any two matching types(2 ints, 2 floats, 2 strings, etc

AAngius Not to mention performance issues

AlkalineLemon•1/30/25, 5:42 PM

hmm, does type casting a lot reduce performance?

Angius•1/30/25, 5:43 PM

Not a lot, but some

Angius•1/30/25, 5:43 PM

Especially when casting from

object

object

Angius•1/30/25, 5:43 PM

object

object

is a reference type. If you store

int

int

— a value type — as an

object

object

, it has to be boxed

Angius•1/30/25, 5:43 PM

Then, when casting back to

int

int

it needs to be unboxed

Angius•1/30/25, 5:43 PM

Both boxing and unboxing do impact performance

AAngius `object` is a reference type. If you store `int` — a value type — as an `object`...

AlkalineLemon•1/30/25, 5:46 PM

so, to store a value type in a reference type(like object). You have to put your value type in the

cap5lut•1/30/25, 5:47 PM

the most crucial part is imo the type safety.
could break at any time for the non-generic types if something else sneaked its way in.
this could for example be a boxed

byte

byte

as well (and yes that would throw)

AlkalineLemon•1/30/25, 5:47 PM

and when you want to get the value type back, you have to take it out of the

object

object

i can see that adding a ton of overhead

MODiX•1/30/25, 5:49 PM

cap5lut

REPL Result: Failure

Exception: InvalidCastException

Compile: 291.560ms | Execution: 20.593ms | React with ❌ to remove this embed.

cap5lut•1/30/25, 6:01 PM

to answer

What would happen without generics?

generic type parameters make classes/structs/interfaces/methods sort of like templates, in a safe manner but keep it DRY.

without generics, you basically have two options:
1) use some horribly slow generalized collection like the mentioned or
2) repeat your code a lot of times, like writing a , a , , etc.

taking collections as example here:
both approaches have their problems which the other fixes:
1) is basically one code base, so bug fixes apply to all collections, but they are not type safe (thus error prone) and due to stuff like boxing pretty slow.
2) has multiple codes, so applying bug fixes is maintenance hell because u have 135890235 types of the same collection but for different element types. its easy to miss one (thus error prone). on the other hand, each collection type is type safe

FakerOP•1/30/25, 6:04 PM

yeahh, sorry, I was just reading a bit about generics and non-generics thing; from what I've understood:

Generics mainly ensure type safety? We must use generics collection instead of non-generics one, this prevent the overhead of casting an object to the required data type. Also, we don't write code multiple times for different data types as mentioned

FakerOP•1/30/25, 6:04 PM

I've a question, what do we mean by "boxing" and "unboxing", is it same as "Casting" ?

FakerOP•1/30/25, 6:04 PM

we say that when we pass an int to an ArrayList for e.g, that int is "box" into an object

FakerOP•1/30/25, 6:05 PM

and in order to retrieve that value, we need to "unbox" it using casing I think

cap5lut•1/30/25, 6:05 PM

with type safety here i mean btw, that u would get a compile error, so your application wouldnt build at all.
the unsafetiness (is that a word?) would be that its a runtime error that might occur at start up, or maybe causes a random crash of ur application in 3h with a 1% chance (have fun debugging that!)

FFaker I've a question, what do we mean by "boxing" and "unboxing", is it same as "Cast...

cap5lut•1/30/25, 6:06 PM

do u know the difference between value types and reference types?

FakerOP•1/30/25, 6:06 PM

yep

FakerOP•1/30/25, 6:06 PM

value types = store copy of a value directly in memory, like int

FakerOP•1/30/25, 6:06 PM

reference types, we store the referece / memory address, like string/ any object

cap5lut•1/30/25, 6:06 PM

boxing is making a value type a reference type, basically putting it into a box onto the heap

FakerOP•1/30/25, 6:07 PM

ahh ok I see

FakerOP•1/30/25, 6:07 PM

then unboxing is when we take a reference type and make it becomes a value type ? it's no longer on heap but on stack then ?

FFaker then unboxing is when we take a reference type and make it becomes a value type ...

cap5lut•1/30/25, 6:08 PM

sort of yes and sort of no.
you cant magically make any reference type a value type. unboxing is literally just to get back the value that was boxed

FakerOP•1/30/25, 6:09 PM

yeah I see

cap5lut•1/30/25, 6:10 PM

one of the reasons why boxing exists is that for arrays u want all elements to be of the same size

cap5lut•1/30/25, 6:11 PM

so that and are exactly

bytes appart

FakerOP•1/30/25, 6:11 PM

ahhhh

FakerOP•1/30/25, 6:11 PM

I see

Ccap5lut one of the reasons why boxing exists is that for arrays u want all elements to b...

FakerOP•1/30/25, 6:11 PM

was going to ask why

Ccap5lut so that `arr[i]` and `arr[i+1]` are exactly `n` bytes appart

FakerOP•1/30/25, 6:12 PM

but what happens internally? like each element will have same data type no? so they take same space?