Hi,
I want to allocate a buffer which I use in a function which reads data from socket.
So I did as a first line in that function:
static char[] buffer=new char[4096];

The compiler (2.062) complained that it cannot evaluate new char[] at compile time.
I Then tried to move the declaration before function, the same thing happened. Allocating statically sized array bloats the executable.
My idea is to return only a slice of array if less than 4K data was read and prevent new allocation on every read.

So what I am doing wrong or is this not possible?
Thank.

On Wednesday, 20 February 2013 at 08:03:48 UTC, Lubos Pintes wrote:
> Hi,
> I want to allocate a buffer which I use in a function which reads data from socket.
> So I did as a first line in that function:
> static char[] buffer=new char[4096];
>
> The compiler (2.062) complained that it cannot evaluate new char[] at compile time.
> I Then tried to move the declaration before function, the same thing happened. Allocating statically sized array bloats the executable.
> My idea is to return only a slice of array if less than 4K data was read and prevent new allocation on every read.
>
> So what I am doing wrong or is this not possible?
> Thank.

In D (and unlike C++), anything static MUST have an initial state that is statically evaluable. "new char[4096]" is a run-time call, so it cannot be done.

The truth is that this actually isn't much different from C++, which hides an invisible "is_initialized" bool somewhere to make it work.

You can try to run-time initialize your buffer the module constructor, for example. Or just create an accessor to get an initialized buffer:

void getBuffer() @safe nothrow
{
    static char[] buffer;
    if (buffer.empty)
        buffer = new char[4096];
    return buffer;
}

Lubos Pintes:

> Allocating statically sized array bloats the executable.

Because char.init is not '\0'. Try to initialize it with zero:

char[10_000] a = '\0';
void main() {}

Bye,
bearophile

Ok thank you. I see now.
One unrelated question: Why the safe attribute has the at-sign, while nothrow doesn't?
Dňa 20. 2. 2013 11:19 monarch_dodra  wrote / napísal(a):
> On Wednesday, 20 February 2013 at 08:03:48 UTC, Lubos Pintes wrote:
>> Hi,
>> I want to allocate a buffer which I use in a function which reads data
>> from socket.
>> So I did as a first line in that function:
>> static char[] buffer=new char[4096];
>>
>> The compiler (2.062) complained that it cannot evaluate new char[] at
>> compile time.
>> I Then tried to move the declaration before function, the same thing
>> happened. Allocating statically sized array bloats the executable.
>> My idea is to return only a slice of array if less than 4K data was
>> read and prevent new allocation on every read.
>>
>> So what I am doing wrong or is this not possible?
>> Thank.
>
> In D (and unlike C++), anything static MUST have an initial state that
> is statically evaluable. "new char[4096]" is a run-time call, so it
> cannot be done.
>
> The truth is that this actually isn't much different from C++, which
> hides an invisible "is_initialized" bool somewhere to make it work.
>
> You can try to run-time initialize your buffer the module constructor,
> for example. Or just create an accessor to get an initialized buffer:
>
> void getBuffer() @safe nothrow
> {
>      static char[] buffer;
>      if (buffer.empty)
>          buffer = new char[4096];
>      return buffer;
> }

Lubos Pintes:

> Why the safe attribute has the at-sign, while nothrow doesn't?

Historical accidents... There is no rhyme & reason in that.

Bye,
bearophile

On Wed, 20 Feb 2013 03:03:49 -0500, Lubos Pintes <lubos.pintes@gmail.com> wrote:

> Hi,
> I want to allocate a buffer which I use in a function which reads data from socket.
> So I did as a first line in that function:
> static char[] buffer=new char[4096];
>
> The compiler (2.062) complained that it cannot evaluate new char[] at compile time.
> I Then tried to move the declaration before function, the same thing happened. Allocating statically sized array bloats the executable.
> My idea is to return only a slice of array if less than 4K data was read and prevent new allocation on every read.
>
> So what I am doing wrong or is this not possible?
> Thank.

What about a fixed sized array?  That won't even incur a heap allocation cost, and makes the function reentrant:

char[4096] buffer = void; // use = void to ensure the compiler doesn't initialize the buffer to all 0xff

-Steve