Some C and C++ projects I am working on use pointers and references extensively: to pass as function arguments, and to return from a function. For function argument I would use `ref`, but for return types, I can't use `ref` and can't return a pointer. What should be the proper way to handle this? Do I have to change function signature (i.e. return type) For example, the following function:

```
//C++ version, from:
https://github.com/bioslaD/fastp/blob/orig/src/read.cpp#L69

Read* Read::reverseComplement(){
	Sequence seq = ~mSeq;
	string qual;
	qual.assign(mQuality.rbegin(), mQuality.rend());
	string strand = (mStrand=="+") ? "-" : "+";
	return new Read(mName, seq, strand, qual);
}

// D version:
Read reverseComplement(){
    Sequence seq = ~mSeq;
    dchar[] qual = cast(dchar[])mQuality.dup;
    reverse(qual);
    string strand = (mStrand=="+") ? "-" : "+";
    Read newRead = new Read(mName, seq, strand, cast(string)qual);
    // return &newRead does not work: returning `& newRead` escapes a reference to local variable newRead
    return newRead;

  }


```
Let's not focus on the function body, I don't know how to handle the return type in cases like this for the D version.

On Thursday, 24 May 2018 at 08:16:30 UTC, biocyberman wrote:
> Some C and C++ projects I am working on use pointers and references extensively: to pass as function arguments, and to return from a function. For function argument I would use `ref`, but for return types, I can't use `ref` and can't return a pointer. What should be the proper way to handle this? Do I have to change function signature (i.e. return type) For example, the following function:
>
> ```
> //C++ version, from:
> https://github.com/bioslaD/fastp/blob/orig/src/read.cpp#L69
>
> Read* Read::reverseComplement(){
> 	Sequence seq = ~mSeq;
> 	string qual;
> 	qual.assign(mQuality.rbegin(), mQuality.rend());
> 	string strand = (mStrand=="+") ? "-" : "+";
> 	return new Read(mName, seq, strand, qual);
> }
>
> // D version:
> Read reverseComplement(){
>     Sequence seq = ~mSeq;
>     dchar[] qual = cast(dchar[])mQuality.dup;
>     reverse(qual);
>     string strand = (mStrand=="+") ? "-" : "+";
>     Read newRead = new Read(mName, seq, strand, cast(string)qual);
>     // return &newRead does not work: returning `& newRead` escapes a reference to local variable newRead
>     return newRead;
>
>   }
>
>
> ```
> Let's not focus on the function body, I don't know how to handle the return type in cases like this for the D version.

it looks like Read is a D class? in which case it already returns by reference.
If you make Read a struct then all you need do is change the function signature from
Read reverseComplement()
to
Read* reverseComplement()

about the function body
use mQuality.dup.representation.reverse;

>     dchar[] qual = cast(dchar[])mQuality.dup;
>     reverse(qual);
>     mQuality = cast(string)qual;

does not do what you want it to do.

On Thursday, 24 May 2018 at 08:58:02 UTC, Nicholas Wilson wrote:
> On Thursday, 24 May 2018 at 08:16:30 UTC, biocyberman wrote:
>> [...]
>
> it looks like Read is a D class? in which case it already returns by reference.
> If you make Read a struct then all you need do is change the function signature from
> Read reverseComplement()
> to
> Read* reverseComplement()
>
> about the function body
> use mQuality.dup.representation.reverse;
>
>>     [...]
>
> does not do what you want it to do.

Thanks for the hints. `Read` in C++ and D are both classes. And the function is inside the class definition itself.

On 2018-05-24 11:10, biocyberman wrote:

> Thanks for the hints. `Read` in C++ and D are both classes. And the function is inside the class definition itself.

In that case specifying the type as `Read` is the correct thing to do. Note that `new` always allocates on the heap and returns a pointer or reference type.

-- 
/Jacob Carlborg

On Thursday, 24 May 2018 at 17:44:19 UTC, Jacob Carlborg wrote:
> On 2018-05-24 11:10, biocyberman wrote:
>
>> Thanks for the hints. `Read` in C++ and D are both classes. And the function is inside the class definition itself.
>
> In that case specifying the type as `Read` is the correct thing to do. Note that `new` always allocates on the heap and returns a pointer or reference type.

Thanks. I did that and it worked correctly.