Re: error: no matching constructor for initialization of 'string_vector'

[Carnë Draug]

On 25 August 2016 at 13:23, Ben Abbott <address@hidden> wrote:
>> On Aug 25, 2016, at 07:09, Carnë Draug <address@hidden> wrote:
>>
>>> On 25 August 2016 at 01:27, Ben Abbott <address@hidden> wrote:
>>> Carne,
>>>
>>> The chagneset below is giving me an error.
>>>
>>>        http://hg.savannah.gnu.org/hgweb/octave/rev/f38e81248556
>>>
>>> libinterp/octave-value/ov-classdef.cc:2275:17: error: no matching 
>>> constructor for initialization of 'string_vector'
>>>  string_vector v (names);
>>>                ^  ~~~~~
>>>
>>> I’m using Apple’s llvm/clang
>>>
>>> Apple LLVM version 7.3.0 (clang-703.0.31)
>>>
>>> Ben
>>
>> I have no idea why your compiler is failing to find the constructor.
>> Is it because it can't decide which constructor to use?  Which ones
>> is it undecided about?
>>
>> Carnë
>
> I'm embarrassed to say that I don't know what a constructor is. I'll do a 
> quick study.
>
> Can give me some background on what your patch is doing?
>

A constructor is a class method that constructs an object of that class.
The name of those methods is the same as the class name.

For example, in Octave, these are constructors:

  p = inputParser (); # construct inputParser object
  a = audiorecorder (fs, nbits, nchannels); # construct audiorecorder object

The change I made replaced the code that was manually constructing
a string_vector, with a string_vector constructor that does the same
thing.


In languages like C++, a class can have more than one constructor, even
with same number of arguments.  The compiler looks at the type of the
arguments and picks the constructor that fits the best.  Sometimes there's
more than one constructor that fits, hence my question about what
constructors is clang considering (gcc error messages mention the
different possibilities so I'm expcting clang to do something similar).

In the case of the string_vector class, these are the constructors available:

    string_vector (void)

    string_vector (octave_idx_type n)

    string_vector (const char *s)

    string_vector (const std::string &s)

    string_vector (const string_vector &s)

    template <template <typename...> class String_Container>
    string_vector (const String_Container<std::string> &lst)

    string_vector (const Array<std::string> &s)

    string_vector (const char *const *s)

    string_vector (const char *const *s, octave_idx_type n)

In the change that's causing issues for clang, the argument is a
std::set<std::string> so I would expect it to use the templated
constructor for String_Container<std::string>.