C#•2y ago•

11 replies

Does structs generate inaccessible copies?

Consider the following large structure for the asked questions

[InlineArray(128)]
public struct x1024BitBuffer 
{
  byte e0;
}

[InlineArray(128)]
public struct x1024BitBuffer 
{
  byte e0;
}

Does a local copy is created when returning from a method?

In my understanding of how structure returning methods are handled, the current method will allocate the necessary memory to store the called method's return within the stack. But, the called method also has it's own stack, so, in the next scenarios, does the struct gets copied back in forth or is it internally passed by reference?

// consider that we marked this method NOT to be inlined
static x1024BitBuffer CreateMe()
  => new()
;

static void Main()
{
  var x = CreateMe();
}

// consider that we marked this method NOT to be inlined
static x1024BitBuffer CreateMe()
  => new()
;

static void Main()
{
  var x = CreateMe();
}

When

Main

Main

invokes

CreateMe

CreateMe

is the structure allocated inside the creator method or does the compiler detects that no one can access it so it makes

new()

new()

allocate directly into

's var memory?

What if the variable is accessed in the creator method but only returned

// consider that we marked this method NOT to be inlined
static x1024BitBuffer CreateMe()
{
  var temp = new x1024BitBuffer ();
  temp[5] = 0x11;
  return temp;
}

static void Main()
{
  var x = CreateMe();
}

// consider that we marked this method NOT to be inlined
static x1024BitBuffer CreateMe()
{
  var temp = new x1024BitBuffer ();
  temp[5] = 0x11;
  return temp;
}

static void Main()
{
  var x = CreateMe();
}

Since the value

temp

temp

is only modified and then returned, is the memory for it allocated in

CreateMe

CreateMe

's stack and then copied to the caller method stack or accessed directly?

Does a a copy of a struct is created when passing through an init accessor?

readonly struct Data
{
  readonly x1024BitBuffer payload;
  
  public x1024BitBuffer Payload 
  {
    init => payload = value;
  }
}

static void Main() 
{
  Data data = new()
  {
    PayLoad = CreateMe()
  };
}

readonly struct Data
{
  readonly x1024BitBuffer payload;
  
  public x1024BitBuffer Payload 
  {
    init => payload = value;
  }
}

static void Main() 
{
  Data data = new()
  {
    PayLoad = CreateMe()
  };
}

When creating a

Data

Data

instance, the IL method

init_Payload

init_Payload

is called. So the stack traces looks something like the following .With that in mind, does the large structure gets copied 2 times or the compiler optmises that in some way?

Main() -> CreateMe() -> init_Payload

Main() -> CreateMe() -> init_Payload

new Data() | => new(); | arg: value

C#•2y ago•

11 replies

𝗝𝗮𝗺𝗲𝘀

Does structs generate inaccessible copies?

Consider the following large structure for the asked questions

[InlineArray(128)]
public struct x1024BitBuffer 
{
  byte e0;
}

[InlineArray(128)]
public struct x1024BitBuffer 
{
  byte e0;
}

Does a local copy is created when returning from a method?

// consider that we marked this method NOT to be inlined
static x1024BitBuffer CreateMe()
  => new()
;

static void Main()
{
  var x = CreateMe();
}

// consider that we marked this method NOT to be inlined
static x1024BitBuffer CreateMe()
  => new()
;

static void Main()
{
  var x = CreateMe();
}

When

Main

Main

invokes

CreateMe

CreateMe

is the structure allocated inside the creator method or does the compiler detects that no one can access it so it makes

new()

new()

allocate directly into

's var memory?

What if the variable is accessed in the creator method but only returned

// consider that we marked this method NOT to be inlined
static x1024BitBuffer CreateMe()
{
  var temp = new x1024BitBuffer ();
  temp[5] = 0x11;
  return temp;
}

static void Main()
{
  var x = CreateMe();
}

// consider that we marked this method NOT to be inlined
static x1024BitBuffer CreateMe()
{
  var temp = new x1024BitBuffer ();
  temp[5] = 0x11;
  return temp;
}

static void Main()
{
  var x = CreateMe();
}

Since the value

temp

temp

is only modified and then returned, is the memory for it allocated in

CreateMe

CreateMe

's stack and then copied to the caller method stack or accessed directly?

Does a a copy of a struct is created when passing through an init accessor?

readonly struct Data
{
  readonly x1024BitBuffer payload;
  
  public x1024BitBuffer Payload 
  {
    init => payload = value;
  }
}

static void Main() 
{
  Data data = new()
  {
    PayLoad = CreateMe()
  };
}

readonly struct Data
{
  readonly x1024BitBuffer payload;
  
  public x1024BitBuffer Payload 
  {
    init => payload = value;
  }
}

static void Main() 
{
  Data data = new()
  {
    PayLoad = CreateMe()
  };
}

When creating a

Data

Data

instance, the IL method

init_Payload

init_Payload

is called. So the stack traces looks something like the following .With that in mind, does the large structure gets copied 2 times or the compiler optmises that in some way?

Main() -> CreateMe() -> init_Payload

Main() -> CreateMe() -> init_Payload

new Data() | => new(); | arg: value

Does structs generate inaccessible copies?

Does a local copy is created when returning from a method?

What if the variable is accessed in the creator method but only returned

Does a a copy of a struct is created when passing through an init accessor?

Does structs generate inaccessible copies?

Does a local copy is created when returning from a method?

What if the variable is accessed in the creator method but only returned

Does a a copy of a struct is created when passing through an init accessor?

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