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digitalmars.D.learn - is there a cleaner way to new a static sized array?

reply BCS <none anon.com> writes:
I need a function that works like the following:


 T* New(T)() { return new T; }



But that also works with static arrays:


 auto i = New!(int)();
 auto a = New!(int[27])();



The cleanest solution I can think of is:


 T* New(T)() { return (new T[1]).ptr; }



but that seems ugly. Any ideas?


-- 
... <IXOYE><
Feb 23 2010
next sibling parent reply daoryn <wef sag.com> writes:
BCS Wrote:


 I need a function that works like the following:
 

 T* New(T)() { return new T; }



 But that also works with static arrays:
 

 auto i = New!(int)();
 auto a = New!(int[27])();



 The cleanest solution I can think of is:
 

 T* New(T)() { return (new T[1]).ptr; }



 but that seems ugly. Any ideas?
 
 




I'm sorry, but I dont understand the purpose. Whats wrong with "T[27] array"?
Unless you want to use the heap but if so, why not just go with dynamic arrays?
Whats the advantage of using static arrays on heap vs dynamic?
Feb 24 2010
parent BCS <none anon.com> writes:
Hello Daoryn,


 BCS Wrote:
 

 I need a function that works like the following:
 

 T* New(T)() { return new T; }



 But that also works with static arrays:
 

 auto i = New!(int)();
 auto a = New!(int[27])();



 The cleanest solution I can think of is:
 

 T* New(T)() { return (new T[1]).ptr; }



 but that seems ugly. Any ideas?
 



 I'm sorry, but I dont understand the purpose. Whats wrong with "T[27] array"?



I need to, under some cases, allocate it array out of a mem-mapped file and 
under others, allocate it off the heap.


 Unless you want to use the heap but if so, why not just go with
 dynamic arrays? Whats the advantage of using static arrays on heap vs
 dynamic?



I expect to have piles of arrays, all the same length where I know their 
length at compile time. In short, aside from the problem of allocating them, 
I have no reason /not/ to use static arrays.

-- 
... <IXOYE><
Feb 24 2010
prev sibling next sibling parent reply FeepingCreature <default_357-line yahoo.de> writes:
On 24.02.2010 05:16, BCS wrote:

 I need a function that works like the following:
 

 T* New(T)() { return new T; }



 But that also works with static arrays:
 

 auto i = New!(int)();
 auto a = New!(int[27])();



 The cleanest solution I can think of is:
 

 T* New(T)() { return (new T[1]).ptr; }



 but that seems ugly. Any ideas?
 
 



The example you listed is the best way.

I'm sorry.
Feb 24 2010
parent reply BCS <none anon.com> writes:
Hello FeepingCreature,


 On 24.02.2010 05:16, BCS wrote:
 

 I need a function that works like the following:
 

 T* New(T)() { return new T; }
 



 

 auto i = New!(int)();
 auto a = New!(int[27])();



 

 T* New(T)() { return (new T[1]).ptr; }
 



 



 



As it happes, it dosn't work as shown:

auto o = New!(Object)(); // oops, typeof(o) == Object*


 I'm sorry.
 



... <IXOYE><
Feb 24 2010
parent reply FeepingCreature <default_357-line yahoo.de> writes:
On 24.02.2010 22:19, BCS wrote:

 Hello FeepingCreature,
 

 On 24.02.2010 05:16, BCS wrote:


 I need a function that works like the following:


 T* New(T)() { return new T; }





 auto i = New!(int)();
 auto a = New!(int[27])();





 T* New(T)() { return (new T[1]).ptr; }









 As it happes, it dosn't work as shown:
 
 auto o = New!(Object)(); // oops, typeof(o) == Object*
 

 I'm sorry.






I assumed that was what you wanted.

Maybe you should just special-case static arrays inside the function with
static if.
Feb 24 2010
parent BCS <none anon.com> writes:
Hello FeepingCreature,


 I assumed that was what you wanted.



Well my bad.


 
 Maybe you should just special-case static arrays inside the function
 with static if.
 



It's still ugly but it's what I'm going with for now.

-- 
... <IXOYE><
Feb 25 2010
prev sibling next sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Tue, 23 Feb 2010 23:16:35 -0500, BCS <none anon.com> wrote:


 I need a function that works like the following:


 T* New(T)() { return new T; }



 But that also works with static arrays:


 auto i = New!(int)();
 auto a = New!(int[27])();



 The cleanest solution I can think of is:


 T* New(T)() { return (new T[1]).ptr; }



 but that seems ugly. Any ideas?



Want to hear something funny?  In developing the array append patch to fix  
stomping, I worried about how memory would be allocated for something like  
this:

int *i = new int;

Simply because I was worried someone would do:

int[] x = i[0..1];
x ~= 4;

If this didn't do the right thing, my array stomping patch might make this  
do the wrong thing.

But as it turns out, the d compiler basically rewrites the line

int * i = new int;

to

int * i = (new int[1]).ptr;

Yep, that's exactly what you did :)  So basically your solution *is* the  
solution to use, because it's what the compiler would do if the syntax was  
allowed.

Some people have proposed recently on the digitalmars.D newsgroup that  
dynamic array allocation with the dimension in the brackets should  
actually allocate a statically-sized array on the heap.  The only allowed  
form for dynamic arrays would be:

int[] x = new int[](1);

Which is currently valid, but would be the only way to allocate dynamic  
arrays.

Although it looks uglier and does not conform to other languages (such as  
java or C#), it allows you to easily allocate a statically-sized array.  I  
hope this change goes through.

Note that you can special case your "New" template for objects using  
static if or using template constraints (if you are on D2)

-Steve
Feb 25 2010
prev sibling parent reply grauzone <none example.net> writes:
BCS wrote:

 I need a function that works like the following:
 

 T* New(T)() { return new T; }



 But that also works with static arrays:
 

 auto i = New!(int)();
 auto a = New!(int[27])();



 The cleanest solution I can think of is:
 

 T* New(T)() { return (new T[1]).ptr; }



 but that seems ugly. Any ideas?
 
 



Does something like this work as expected?

T* New(T)() { static struct X { T x; } return &(new X).x }

(untested)
Feb 25 2010
parent BCS <none anon.com> writes:
Hello grauzone,


 BCS wrote:
 

 I need a function that works like the following:
 

 T* New(T)() { return new T; }
 



 

 auto i = New!(int)();
 auto a = New!(int[27])();



 

 T* New(T)() { return (new T[1]).ptr; }
 



 



 
 T* New(T)() { static struct X { T x; } return &(new X).x }
 
 (untested)



I'm going to guess it works, but it doesn't make anything much cleaner (and 
BTW, I think that static is unneeded).

-- 
... <IXOYE><
Feb 25 2010