Dynamic array creation with default

[Timon Gehr]

On 08/23/2011 03:15 PM, foobar wrote:
> == Quote from bearophile (bearophileHUGS at lycos.com)'s article
>> foobar:
>>> you raise a valid concern but this looks too complicated.
>>> I'd suggest to simplify into only two cases.
>>>
>>> // 1) T.INIT - as you suggested the dimension should be checked
>>> auto foo = new int[][](10, 20); // correct
>>> auto foo1 = new int[][](10); // compilation error
>> Keep in mind that currently this is correct and it generates a 1D dynamic array:
>> auto v = new int[10];
>
> Isn't this an inconsistency in the language?
>
> // Generally speaking, allocates an instance of T on the heap
> auto foo = new T;
>
> However, "int[10]" and "new int[10]" are different types.

int and typeof(new int) are different types too.


>
>>> // 2) function of the array dimension
>>> auto bar = new int[][](10, 20, (int x, int y) { return x*y; } );
>>>
>>> // if you want a default value just use:
>>> auto bar1 = new int[][](10, 20, { return 3; } );
>>>
>>> For fixed-sized arrays the function would be CTFE-able.
>> This is more complex than my suggestions :-)
>> The most common case is the initialization with a constant value. I'd like this
> case to be as efficient as possible, so I don't like the { return 3; }.
>
> This syntax could be simplified if we drop "return" as suggested in another
> thread. Also, couldn't we employ "lazy" for this? I don't remember how it works,
> does it accept a value on the call-site?
> On the other hand, I dislike the named-parameter suggestion. Named parameters
> indicate in my eyes a design bug.
>
>> The case with a more complex delegate is interesting to initialize constant arrays:
>> immutable m = new int[][](10, 20, (int x, int y){ return x*y; });
>> But in my opinion this is not a so common operation. And it's not able to
> replace Python-style array comps:
>> foo = [x ** x for x in lazyIterable]
>> So I don't like your proposals.
>> Maybe dsimcha will give a Phobos function to allocate&  initialize a nD array
> with a given const value.
>> Bye,
>> bearophile
>