The analogue of "fill-pointer" in D
Steven Schveighoffer via Digitalmars-d-learn
digitalmars-d-learn at puremagic.com
Mon May 18 10:14:46 PDT 2015
On 5/18/15 6:24 AM, Dennis Ritchie wrote:
> On Monday, 18 May 2015 at 10:14:33 UTC, Kagamin wrote:
>> On Monday, 18 May 2015 at 08:21:38 UTC, Dennis Ritchie wrote:
>>> Hi,
>>>
>>> In Common Lisp, there is such a thing as a fill-pointer (Example 5):
>>> http://www.tutorialspoint.com/lisp/lisp_arrays.htm
>>>
>>> Does D some equivalent?
>>
>> Data stored in the array is indicated by the array length property,
>> use capacity to figure out extra available space:
>> http://dlang.org/phobos/object.html#.capacity
>
> No, afraid not. Function capacity is not an analogue of fill-pointers!
capacity is analogous to the number of elements in the vector (as
returned by array-dimension according to
https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node162.html).
arr.length is analogous to the fill pointer.
example:
int[] arr = new int[](5);
assert(arr.capacity > 5);
assert(arr.length == 5);
arr.reserve(100); // expand arr memory block to be able to hold *at
least* 100 ints
assert(arr.capacity >= 100);
assert(arr.length == 5);
auto ptr = arr.ptr; // for later assert
arr ~= 1; // increment length by 1, 'fill in' tail of array with '1'
// this should demonstrate how it works
assert(arr.length == 6); // new fill pointer
assert(arr.capacity >= 100); // capacity unchanged
assert(arr.ptr is ptr); // array still lives in same memory block
Apologies for not translating to lisp, I don't know it.
-Steve
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