Comments on: Function Aliases In C++

By: leni536

leni536 — Fri, 19 Oct 2018 08:16:00 +0000

One can’t alias to operators with auto variables. One possible use case would be to alias user-defined literals to different ud-suffix as provided by a library. It could be needed to avoid ud-suffix clashes from different libraries.
Also the auto approach doesn’t work with overloaded function types due to ambiguity.

Note that the macro approach works for both cases above (it doesn’t assume that lowLevelF is actually a template). But the macro approach only works for function templates where all template arguments can be deduced from the parameters. In fact it only works for template functions where the template arguments are exactly the parameter types. It can’t be used to alias std::make_unique for example. I wonder if a more general macro is possible, I can’t come up with one. It also can’t be used in function scope as template functions can’t be declared there (I still don’t know why it’s not lifted already).

I don’t say that these approaches are not useful, I just state some shortcomings. Obviously one can fall back to the one-liner approach if all these fail.

By: Jonathan Boccara

Jonathan Boccara — Sun, 09 Sep 2018 16:15:00 +0000

In reply to Lê Huy. Hi Lê, by looking at the code, it seems that the problem is that you're trying to alias a class method, and I don't think you can do this in C++. Note I'm not 100% sure about this since I couldn't find any documentation about it.

By: Lê Huy

Lê Huy — Sat, 08 Sep 2018 14:23:00 +0000

In reply to Lê Huy.

*** For case 2 https://uploads.disquscdn.com/images/441ce3785d27842b8c0c8ad2527c8f8628441b481b2c212bfd920e7b2abd7b54.png

By: Lê Huy

Lê Huy — Sat, 08 Sep 2018 14:22:00 +0000

In reply to Lê Huy.

*** For case 1 https://uploads.disquscdn.com/images/09033a32b16b9f1c0245d7da395f3dee0e257916746a516cc4a59ba129fe0bc9.png

By: Lê Huy

Lê Huy — Sat, 08 Sep 2018 14:11:00 +0000

In reply to Lê Huy.

When I try:
template using reset = typename option::array::initialize;
…
reset();

I get error:
1) ‘reset’: use of alias template requires template argument list
2) syntax error: unexpected type ‘reset’

By: Lê Huy

Lê Huy — Sat, 08 Sep 2018 14:05:00 +0000

// a.h
namespace option {
template
class array
{
public:
int _data[_Size];
protected:
void initialize();
public:
array();
virtual ~array();
};
}
// a.cpp
template const auto& reset = option::array::initialize;
template option::array::~array()
{
reset();
}
I get error:
1) ‘reset’: use of a variable template requires template argument list
2) ‘reset’: cannot be used before it is initialized
How can I fix it sir?

By: Jonathan Boccara

Jonathan Boccara — Sun, 29 Oct 2017 00:23:00 +0000

In reply to dutiona. Well spotted, the compilation error appears indeed with several parameters. Typo fixed, thanks!

By: Jonathan Boccara

Jonathan Boccara — Sun, 29 Oct 2017 00:15:00 +0000

In reply to Risto Lankinen. Well this is not supposed to work: using makes aliases on types, and not on functions.

By: dutiona

dutiona — Fri, 27 Oct 2017 20:27:00 +0000

std::forward(args…) is wrong.
std::forward(args)… is correct.
Don’t forget to compile the code you publish.

By: Risto Lankinen

Risto Lankinen — Fri, 27 Oct 2017 16:18:00 +0000

How about…

using newId = newIdFromDatabase;

… ?