I have a function that takes a large matrix as an out parameter.
Is there a way to do `=void` for an out parameter like there is for is for a plain declaration?
enum M = 2600;
void f() {
    float[M] mean = void; // works as expected, mean is left uninitialised
}

void g(out float[M][M] corr) // works but assigns twice
{
    corr[] = float.init; // compiler inserted

    // assign to each value of corr
}

//Error: found ')' when expecting '.' following void
void h(out float[M][M] corr = void)
{

}

is there a way to not assign to out variables?

On Saturday, 19 August 2017 at 06:20:28 UTC, Nicholas Wilson wrote:
> I have a function that takes a large matrix as an out parameter.
> Is there a way to do `=void` for an out parameter like there is for is for a plain declaration?
> enum M = 2600;
> void f() {
>     float[M] mean = void; // works as expected, mean is left uninitialised
> }
>
> void g(out float[M][M] corr) // works but assigns twice
> {
>     corr[] = float.init; // compiler inserted
>
>     // assign to each value of corr
> }
>
> //Error: found ')' when expecting '.' following void
> void h(out float[M][M] corr = void)
> {
>
> }
>
> is there a way to not assign to out variables?

Try 'ref' instead of 'out'.

On Saturday, 19 August 2017 at 06:23:10 UTC, Igor Shirkalin wrote:
> On Saturday, 19 August 2017 at 06:20:28 UTC, Nicholas Wilson wrote:
>> I have a function that takes a large matrix as an out parameter.
>> Is there a way to do `=void` for an out parameter like there is for is for a plain declaration?
>> enum M = 2600;
>> void f() {
>>     float[M] mean = void; // works as expected, mean is left uninitialised
>> }
>>
>> void g(out float[M][M] corr) // works but assigns twice
>> {
>>     corr[] = float.init; // compiler inserted
>>
>>     // assign to each value of corr
>> }
>>
>> //Error: found ')' when expecting '.' following void
>> void h(out float[M][M] corr = void)
>> {
>>
>> }
>>
>> is there a way to not assign to out variables?
>
> Try 'ref' instead of 'out'.

Hmm, I could, but ref doesn't signal intention like out does.

On Saturday, 19 August 2017 at 06:20:28 UTC, Nicholas Wilson wrote:
> is there a way to not assign to out variables?

I don't think so. Is there a good reason not to return the matrix directly (taking advantage of in-place construction)?

float[M][M] f()
{
    float[M][M] mean = void;
    // init
    return mean;
}

On 8/18/2017 11:24 PM, Nicholas Wilson wrote:
> On Saturday, 19 August 2017 at 06:23:10 UTC, Igor Shirkalin wrote:
>> On Saturday, 19 August 2017 at 06:20:28 UTC, Nicholas Wilson wrote:
>>> I have a function that takes a large matrix as an out parameter.
>>> Is there a way to do `=void` for an out parameter like there is for is for a plain declaration?
>>> enum M = 2600;
>>> void f() {
>>>     float[M] mean = void; // works as expected, mean is left uninitialised
>>> }
>>>
>>> void g(out float[M][M] corr) // works but assigns twice
>>> {
>>>     corr[] = float.init; // compiler inserted
>>>
>>>     // assign to each value of corr
>>> }
>>>
>>> //Error: found ')' when expecting '.' following void
>>> void h(out float[M][M] corr = void)
>>> {
>>>
>>> }
>>>
>>> is there a way to not assign to out variables?
>>
>> Try 'ref' instead of 'out'.
> 
> Hmm, I could, but ref doesn't signal intention like out does.

True. Please file an enhancement request.

On Saturday, 19 August 2017 at 23:05:26 UTC, Walter Bright wrote:
> On 8/18/2017 11:24 PM, Nicholas Wilson wrote:
>> Hmm, I could, but ref doesn't signal intention like out does.
>
> True. Please file an enhancement request.

https://issues.dlang.org/show_bug.cgi?id=17765

I also realised that ref won't error on reads from the parameter, whereas out does.