C#•2mo ago

C# array init

if I initialize an array of structs, which constructor does it use if any?

MyStruct[,] array = new MyStruct[2, 3];

struct MyStruct {
  public MyStruct() {
    // ctor
  }
  
  public MyStruct(int x) {
    // another ctor
  }
}

MyStruct[,] array = new MyStruct[2, 3];

struct MyStruct {
  public MyStruct() {
    // ctor
  }
  
  public MyStruct(int x) {
    // another ctor
  }
}

57 Replies

MODiX•2mo ago

Angius

REPL Result: Success

MyStruct[,] array = new MyStruct[2, 3];

struct MyStruct {
  public MyStruct() {
    Console.WriteLine("one");
  }
  
  public MyStruct(int x) {
    Console.WriteLine("two");
  }
}

MyStruct[,] array = new MyStruct[2, 3];

struct MyStruct {
  public MyStruct() {
    Console.WriteLine("one");
  }
  
  public MyStruct(int x) {
    Console.WriteLine("two");
  }
}

Compile: 464.482ms | Execution: 35.715ms | React with ❌ to remove this embed.

Angius•2mo ago

Neither

שלום אני בן עמי•2mo ago

can I make it use any of them?

Angius•2mo ago

What exactly do you want to achieve?

שלום אני בן עמי•2mo ago

perhaps passing a generating function that will run for each item in the array not having to write a for loop under the new MyStruct[]

Angius•2mo ago

Well, yeah But, what, you want the array to be pre-filled with structs and those structs with default values?

שלום אני בן עמי•2mo ago

yeah, i figured creating a default constructor would do but ig C# never fails to confuse me

Angius•2mo ago

I guess C# just uses some other, magic constructor

Servator•2mo ago

 public string this[int index] { }

 public string this[int index] { }

Are you looking for this?

Angius•2mo ago

And fills the properties of the struct with default values

Angius•2mo ago

Angius•2mo ago

Not even assigning a default value to a property works So just treat all the entries in the array as undefined, in whatever way a struct can be undefined

Jimmacle•2mo ago

the default for value types is zeroed out, not undefined same way that the default for reference types is null (0)

230V•2mo ago

A loop, an initializer or any other way of initializing elements used later is required here

שלום אני בן עמי•2mo ago

well that seems dumb imo maybe im dumb and I can't comprehend it

Jimmacle•2mo ago

Enumerable.Repeat(new MyStruct(), 100).ToArray() :when:

230V•2mo ago

Something like Array.Fill(array, new MyStruct()); too I think

Jimmacle•2mo ago

yeah, if you already have the array

שלום אני בן עמי•2mo ago

both of those dont work on 2d arrays ✨ aint C# great

Jimmacle•2mo ago

2d arrays aren't common anyway in my experience but if you need them, just write a loop

שלום אני בן עמי•2mo ago

doesn't really matter to be fair

Jimmacle•2mo ago

3 lines

שלום אני בן עמי•2mo ago

i've seen how Func is defined still isn't great

Jimmacle•2mo ago

Func is just a delegate, there isn't really anything to it just a bunch of variations to account for different numbers of arguments

שלום אני בן עמי•2mo ago

still looks like this though:

Func<TResult>
Func<T,TResult>
Func<T1,T2,TResult>
Func<T1,T2,T3,TResult>
Func<T1,T2,T3,T4,TResult>
Func<T1,T2,T3,T4,T5,TResult>
Func<T1,T2,T3,T4,T5,T6,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14,T15,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14,T15,T16,TResult>

Func<TResult>
Func<T,TResult>
Func<T1,T2,TResult>
Func<T1,T2,T3,TResult>
Func<T1,T2,T3,T4,TResult>
Func<T1,T2,T3,T4,T5,TResult>
Func<T1,T2,T3,T4,T5,T6,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14,T15,TResult>
Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14,T15,T16,TResult>

Jimmacle•2mo ago

and? variadic generic arguments aren't a thing

שלום אני בן עמי•2mo ago

I know, but this still sucks

Jimmacle•2mo ago

¯\_(ツ)_/¯

שלום אני בן עמי•2mo ago

it's like waiting for a bus when you have no roof and it rains you can't evade the situation but it sucks

Jimmacle•2mo ago

i don't think about this at all personally it doesn't affect anything i do

Angius•2mo ago

I really have no idea why it bothers you tbh

230V•2mo ago

//shit happens

Angius•2mo ago

The lack of Array.Fill for n-dim arrays, sure, I understand But how Func types are defined...?

שלום אני בן עמי•2mo ago

well, it doesn't make me feel better about C# tbh I usually write python, functional languages and sometimes C++. Now I gotta use C# and it feels weird i gotta have something to cope about

Jimmacle•2mo ago

i mean, when's the last time the way func was defined interfered with you using C# to solve a problem

שלום אני בן עמי•2mo ago

what about my 17-argument function?

Jimmacle•2mo ago

then write your own delegate

Angius•2mo ago

Jimmacle•2mo ago

if you have a 17 argument function that's probably an issue in itself anyway

Petris•2mo ago

https://learn.microsoft.com/en-us/dotnet/api/system.array.initialize?view=net-8.0

Array.Initialize Method (System)

Initializes every element of the value-type Array by calling the parameterless constructor of the value type.

Jimmacle•2mo ago

16 is more than enough for any reasonable use case i've probably never needed more than 3 or 4 at that point you should write your own delegate just for self-documenting purposes

Angius•2mo ago

Yeah, I'd imagine at this point you would really want all of those params named

שלום אני בן עמי•2mo ago

thank you

Petris•2mo ago

just note that it'll be slower than a simple loop

שלום אני בן עמי•2mo ago

why

Petris•2mo ago

or actually, not sure about a loop on an MD one

שלום אני בן עמי•2mo ago

why would it be though?

Jimmacle•2mo ago

https://source.dot.net/#System.Private.CoreLib/src/System/Array.CoreCLR.cs,628 because it's more than just a loop

שלום אני בן עמי•2mo ago

but it's not a lot more than just a loop

Jimmacle•2mo ago

you asked why it would be slower and that's why

שלום אני בן עמי•2mo ago

but it's like 3 if checks

Angius•2mo ago

All three of which cost some performance Not much, but some So, yes, it would be marginally slower than a simple loop

שלום אני בן עמי•2mo ago

for my not performence sensitive project it will suffice thanks though

Petris•2mo ago

there's also the fact that it calls the constructor through a pointer there which will be slower

שלום אני בן עמי•2mo ago

how does it call the function otherwise? the compiler still gonna calculate the offset for the vtable and use it to call the method isnt it? ig not the vtable cause no dynamic dispatch is needed but the method table of the struct

Jimmacle•2mo ago

you could just benchmark the options

שלום אני בן עמי•2mo ago

i might

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C# array init