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digitalmars.D.learn - I feel the dynamic array .sizeof property is kind of a bait and switch

reply WhatMeForget <kheaser gmail.com> writes:
Static Arrays have property
.sizeof which returns the array length multiplied by the number 
of bytes per array element.

Dynamic Arrays have property
.sizeof which returns the size of the dynamic array reference, 
which is 8 in 32-bit builds and 16 on 64-bit builds.

Why not have dynamic arrays with a .sizeof identical to static 
arrays and say another property called .sizeref which handles the 
32 or 64 bit references.

Maybe Phobos has something that I'm not aware of?

I've hand rolled a function which is working for me currently, 
but with my coding ability, I'd feel much safer with something 
official :)

It just seems like something this basic regarding dynamic arrays 
should just be built-in.
Jul 25 2017
next sibling parent reply Mike Parker <aldacron gmail.com> writes:
On Wednesday, 26 July 2017 at 02:24:06 UTC, WhatMeForget wrote:

 Static Arrays have property
 .sizeof which returns the array length multiplied by the number 
 of bytes per array element.

 Dynamic Arrays have property
 .sizeof which returns the size of the dynamic array reference, 
 which is 8 in 32-bit builds and 16 on 64-bit builds.

 Why not have dynamic arrays with a .sizeof identical to static 
 arrays and say another property called .sizeref which handles 
 the 32 or 64 bit references.

 Maybe Phobos has something that I'm not aware of?

 I've hand rolled a function which is working for me currently, 
 but with my coding ability, I'd feel much safer with something 
 official :)

 It just seems like something this basic regarding dynamic 
 arrays should just be built-in.


Because .sizeof has nothing to do with how many elements are in 
the array. It tells you how much space the array itself takes up. 
With static arrays, the memory for the elements if part of the 
array itself, so it is counted in the size. For dynamic arrays, 
it is not. For .sizeof to report the size of the allocated memory 
would be incorrect.
Jul 25 2017
parent reply WhatMeWorry <kheaser gmail.com> writes:
On Wednesday, 26 July 2017 at 02:31:33 UTC, Mike Parker wrote:

 On Wednesday, 26 July 2017 at 02:24:06 UTC, WhatMeForget wrote:

 [...]


 Because .sizeof has nothing to do with how many elements are in 
 the array. It tells you how much space the array itself takes 
 up.


Totally agree.  .length returns the the number of array elements.


 With static arrays, the memory for the elements if part of the 
 array itself, so it is counted in the size. For dynamic arrays, 
 it is not. For .sizeof to report the size of the allocated 
 memory would be incorrect.


OK, Then I assume the critical thing is that dynamic arrays 
memory is
not part of the array itself.  But is this a deal breaker?
Jul 26 2017
parent Mike Parker <aldacron gmail.com> writes:
On Wednesday, 26 July 2017 at 16:27:57 UTC, WhatMeWorry wrote:

 On Wednesday, 26 July 2017 at 02:31:33 UTC, Mike Parker wrote:


 With static arrays, the memory for the elements if part of the 
 array itself, so it is counted in the size. For dynamic 
 arrays, it is not. For .sizeof to report the size of the 
 allocated memory would be incorrect.


 OK, Then I assume the critical thing is that dynamic arrays 
 memory is
 not part of the array itself.  But is this a deal breaker?


A deal breaker for what? For making sizeof return the amount of 
memory allocated? Yes. It's the same behavior in C and C++:

float verts[3];
assert(sizeof(verts) == (sizeof(float) * 3));

float *verts = malloc(sizeof(float)*3);
assert(sizeof(verts) == sizeof(void*));
Jul 26 2017
prev sibling parent reply Adam D. Ruppe <destructionator gmail.com> writes:
On Wednesday, 26 July 2017 at 02:24:06 UTC, WhatMeForget wrote:

 Static Arrays have property
 .sizeof which returns the array length multiplied by the number 
 of bytes per array element.

 Dynamic Arrays have property
 .sizeof which returns the size of the dynamic array reference, 
 which is 8 in 32-bit builds and 16 on 64-bit builds.


Both actually already do exactly the same thing: .sizeof returns 
the size of the variable. Same thing with pointers, class 
references, and everything else.


 I've hand rolled a function which is working for me currently, 
 but with my coding ability, I'd feel much safer with something 
 official :)


You could also do (cast(ubyte[]) array).length.


 It just seems like something this basic regarding dynamic 
 arrays should just be built-in.


What are you using it for?
Jul 25 2017
parent WhatMeWorry <kheaser gmail.com> writes:
On Wednesday, 26 July 2017 at 02:32:07 UTC, Adam D. Ruppe wrote:

 I've hand rolled a function which is working for me currently, 
 but with my coding ability, I'd feel much safer with something 
 official :)


 You could also do (cast(ubyte[]) array).length.


This was my (way over complicated) attempt at the same thing. 
I'll blame my verbosity because I was trying to teach myself 
about templates and constraints at the time :)

/+
There is a special type of array which acts as a wildcard that 
can hold arrays of any kind, declared as void[].  The .length of 
a void array is the length of the data in
bytes rather than the number of elements in its original type. "
+/

int arrayByteSize(T)(T someArray) if (isDynamicArray!(T))
{
     ubyte[] arr = cast(ubyte[]) someArray;
     return cast(int) arr.length;
}


 It just seems like something this basic regarding dynamic 
 arrays should just be built-in.


 What are you using it for?


glBufferData(GL_ARRAY_BUFFER, vertices.arrayByteSize, 
vertices.ptr, GL_STATIC_DRAW);

I find that openGL uses array buffers all over the place.

I just keep going back to the idea that such low level 
functionality should be inherent in either the language or 
Phobos.  If that is even possible.
Jul 26 2017