spir denis.spir at
Sat Nov 13 12:57:50 PST 2010

On Fri, 12 Nov 2010 08:03:26 -0500
"Steven Schveighoffer" <schveiguy at> wrote:

> Pelle, I spent all this time helping him, and you swoop in with the answer  
> :)
> Yes, he is right, you need to dup the patterns argument.  It is something  
> I very recently discovered.

Wow, first thought dup did not solve the issue, but it fact I had introduced another bug in the meanyrime ;-) All works fine, now. I'll be able to restart working on this. D soon has a prototype for a PEG lib.

> Here is what happens:
> void foo(int[] arg...) {}
> foo(1,2,3);
> What the compiler does is push 1, 2, and 3 onto the stack, then passes in  
> a dynamic array reference to that stack data.  It does this because heap  
> allocations are much more expensive than stack allocations.  When you just  
> "save" the data, it is no longer valid.  The reason the code all works  
> within the List constructor is because that is the stack frame where the  
> array is pushed onto the stack.


> Note, you can do foo([1,2,3]), and you will be wasting time duping, but I  
> have found a solution to that, overloading:
> void foo(int[] arg) {}
> If you pass in an array, then the second overload is used, if you pass in  
> individual arguments the first overload is used.

All right. I find a bit strange that the compiler accepts f([1,2,3]) when the declaration reads eg void f(int[] ints...). Anyway, it cannot harm, I guess.

> Essentially, if you change your line above to:
> this.patterns = patterns.dup;

Works, but I don't understand why: isn't the duplicate also allocated on the stack? I mean, dup is supposed to just duplicate, isn't it? what does it give to the new structure that the original one hasn't? I thought I would have to do for instance:
	ints[] x;
	void f(int[] ints...) {
	  x.length = ints.length;   // allocate new area on the heap
	  x[] = ints[];             // copy elements in there

> All is well, you should be good.


> -Steve

Thank you and Pelle for your help,
-- -- -- -- -- -- --
vit esse estrany ☣

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