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After some investigation, looks like the behavior initializing variables
follows some well-defined convention.

For single element:

    new int; // random
    new int(); // 0 (default initializer)
    new int(23); // 23 (copy initializer)

    new Test; // default contructor
    new Test(...); // X constructor (overload-chosen)

This makes a lot of sense, until you try to apply the same logic on arrays:

    new int[10]; // all random - OK
    new int[10](); // all 0 (default initializer) - OK
    new int[10](23); // all 23 (copy initializer on all) - NOT IMPLEMENTED

    new Test[10]; // default contructors - OK
    new Test[10](); // default contructors - OK
    new Test[10](...); // X constructor on all (overload-chosen) - NOT
IMPLEMENTED

My logic says that you can make some assumptions:
If a type can be constructed using `T(Args..)` then every element from the
array can be constructed. There is no reason to not allow `T[N](Args...)`
syntax.

Why this feature doesn't exist? It would be very nice to allow

    new int[10](23); // all 23
    new Test[10]("asd", 123); // construct all using Test("asd", 123)

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<div dir=3D"ltr">After some investigation, looks like the behavior initiali=
zing variables follows some well-defined convention.<br><br>For single elem=
ent:<br><br>=C2=A0=C2=A0=C2=A0 new int; // random<br>=C2=A0=C2=A0=C2=A0 new=
 int(); // 0 (default initializer)<br>=C2=A0=C2=A0=C2=A0 new int(23); // 23=
 (copy initializer)<br><br>=C2=A0=C2=A0=C2=A0 new Test; // default contruct=
or<br>=C2=A0=C2=A0=C2=A0 new Test(...); // X constructor (overload-chosen)<=
br><br>This makes a lot of sense, until you try to apply the same logic on =
arrays:<br><br>=C2=A0=C2=A0=C2=A0 new int[10]; // all random - OK<br>=C2=A0=
=C2=A0=C2=A0 new int[10](); // all 0 (default initializer) - OK<br>=C2=A0=
=C2=A0=C2=A0 new int[10](23); // all 23 (copy initializer on all) - NOT IMP=
LEMENTED<br><br>=C2=A0=C2=A0=C2=A0 new Test[10]; // default contructors - O=
K<br>=C2=A0=C2=A0=C2=A0 new Test[10](); // default contructors - OK<br>=C2=
=A0=C2=A0=C2=A0 new Test[10](...); // X constructor on all (overload-chosen=
) - NOT IMPLEMENTED<br><br>My logic says that you can make some assumptions=
:<br>If a type can be constructed using `T(Args..)` then every element from=
 the array can be constructed. There is no reason to not allow `T[N](Args..=
..)` syntax.<br><br>Why this feature doesn&#39;t exist? It would be very nic=
e to allow<br><br>=C2=A0=C2=A0=C2=A0 new int[10](23); // all 23<br>=C2=A0=
=C2=A0=C2=A0 new Test[10](&quot;asd&quot;, 123); // construct all using Tes=
t(&quot;asd&quot;, 123)<br></div>

<p></p>

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om/a/isocpp.org/d/msgid/std-proposals/5388a0fb-588a-47b5-aebe-338a2d73c84e%=
40isocpp.org?utm_medium=3Demail&utm_source=3Dfooter">https://groups.google.=
com/a/isocpp.org/d/msgid/std-proposals/5388a0fb-588a-47b5-aebe-338a2d73c84e=
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Other discussion threads:

https://stackoverflow.com/questions/48610895/allow-calling-any-contructor-for-all-array-elements
https://www.reddit.com/r/cpp/comments/7v80pe/why_doesnt_c_allow_calling_any_contructor_for_all/

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<div dir=3D"ltr"><div>Other discussion threads:</div><div><br></div><div>ht=
tps://stackoverflow.com/questions/48610895/allow-calling-any-contructor-for=
-all-array-elements</div><div>https://www.reddit.com/r/cpp/comments/7v80pe/=
why_doesnt_c_allow_calling_any_contructor_for_all/<br></div></div>

<p></p>

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om/a/isocpp.org/d/msgid/std-proposals/adec0f91-9155-4cd6-8bfa-310c5a02d291%=
40isocpp.org?utm_medium=3Demail&utm_source=3Dfooter">https://groups.google.=
com/a/isocpp.org/d/msgid/std-proposals/adec0f91-9155-4cd6-8bfa-310c5a02d291=
%40isocpp.org</a>.<br />

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.

On 2018-02-04 18:29, Iv=C3=A1n Sanz wrote:
> After some investigation, looks like the behavior initializing variables=
=20
> follows some well-defined convention.
>=20
> For single element:
>=20
>  =C2=A0=C2=A0=C2=A0 new int; // random
>  =C2=A0=C2=A0=C2=A0 new int(); // 0 (default initializer)
>  =C2=A0=C2=A0=C2=A0 new int(23); // 23 (copy initializer)
>=20
>  =C2=A0=C2=A0=C2=A0 new Test; // default contructor
>  =C2=A0=C2=A0=C2=A0 new Test(...); // X constructor (overload-chosen)
>=20
> This makes a lot of sense, until you try to apply the same logic on array=
s:
>=20
>  =C2=A0=C2=A0=C2=A0 new int[10]; // all random - OK
>  =C2=A0=C2=A0=C2=A0 new int[10](); // all 0 (default initializer) - OK
>  =C2=A0=C2=A0=C2=A0 new int[10](23); // all 23 (copy initializer on all) =
- NOT IMPLEMENTED
>=20
>  =C2=A0=C2=A0=C2=A0 new Test[10]; // default contructors - OK
>  =C2=A0=C2=A0=C2=A0 new Test[10](); // default contructors - OK
>  =C2=A0=C2=A0=C2=A0 new Test[10](...); // X constructor on all (overload-=
chosen) - NOT=20
> IMPLEMENTED
>=20
> My logic says that you can make some assumptions:
> If a type can be constructed using `T(Args..)` then every element from=20
> the array can be constructed. There is no reason to not allow=20
> `T[N](Args...)` syntax.
>=20
> Why this feature doesn't exist? It would be very nice to allow
>=20
>  =C2=A0=C2=A0=C2=A0 new int[10](23); // all 23
>  =C2=A0=C2=A0=C2=A0 new Test[10]("asd", 123); // construct all using Test=
("asd", 123)
>=20

This might fall under the "Don't try to fix C-style arrays"-principle,=20
which got us std::vector and std::array as replacements.

If you can do

    new int[10](23); // all 23

then why can't we then do this without 'new'?

    int a[10](23);  // What happens here?

or

    int a[10] =3D {23};  //??



     Bo Persson


--=20
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..org/d/msgid/std-proposals/p57je9%24ee9%241%40blaine.gmane.org.

.

On Sunday, 4 February 2018 10:31:34 PST Bo Persson wrote:
> then why can't we then do this without 'new'?
>
>     int a[10](23);  // What happens here?
>
> or
>
>     int a[10] = {23};  //??

The latter one *can* be done. It's a valid syntax.

But it initialises the first element to 23 and the rest are default
initialised.

--
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
   Software Architect - Intel Open Source Technology Center



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