• Timothee Cour (10/10) Sep 17 2013 This may have been discussed before, but I'm not sure whether this is a ...
• monarch_dodra (50/62) Sep 18 2013 There is no "argument-less constructor" in D. "Struct()" is just
• H. S. Teoh (8/29) Sep 18 2013 [...]
• Gary Willoughby (4/16) Sep 18 2013 You are not passing a value to the constructor. Use auto

Timothee Cour <thelastmammoth gmail.com> writes:

This may have been discussed before, but I'm not sure whether this is a bug
or not. In any case it's a bit confusing.

struct Foo2{
  this(T...)(T args){
    assert(0);
  }
}

void main(){
  auto a2=Foo2();//doesn't call assert(0) (ie this(T...) not called)
}

"monarch_dodra" <monarchdodra gmail.com> writes:

On Wednesday, 18 September 2013 at 05:28:41 UTC, Timothee Cour 
wrote:
 This may have been discussed before, but I'm not sure whether 
 this is a bug
 or not. In any case it's a bit confusing.

 struct Foo2{
   this(T...)(T args){
     assert(0);
   }
 }

 void main(){
   auto a2=Foo2();//doesn't call assert(0) (ie this(T...) not 
 called)
 }

There is no "argument-less constructor" in D. "Struct()" is just 
shorthand for "Struct.init" (bar a few exceptional exceptions: 
 disabled this() and static opCall).

AFAIK, D decided to not have "default" constructors, as it goes 
against a few other features (compile time known init state, 
compile time statics). However, not having a constructor which 
has "0 arguments" is a gratuitous historical limitation.

Chances are it won't change any time soon (or ever).

Workarounds include:
//----
//
Calling "__ctor" explicitly:
Foo2 foo2;
foo2.__ctor();
(IMO god awful solution)

//----
//
Using static opCall instead of constructor:
struct Foo2
{
   Foo2 static opCall(T...)(T args)
   {
     Foo2 ret;
     //Do something.
     return ret;
   }
}
Foo2 foo2 = Foo2(); //Calls opCall
A bit hackish, but works. Unfortunately, this is not a 
"construction" sequence, so you won't be able to use it with 
emplace, for example.

//----
//
A non-member free function. Similar to static opCall, but a bit 
less hackish. Just create a free function (usually named the same 
as your struct, but lowercased).
This is also used a lot in Phobos, as it can prevent direct use 
of the struct:

private struct Foo2Result
{

}

public auto foo2(T...)(T args)
{
     Foo2 ret;
     //Do something.
     return ret;
}

auto myFoo2 = foo2(); //Calls the function.

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Wed, Sep 18, 2013 at 10:12:04AM +0200, monarch_dodra wrote:
 On Wednesday, 18 September 2013 at 05:28:41 UTC, Timothee Cour
 wrote:
This may have been discussed before, but I'm not sure whether this is
a bug or not. In any case it's a bit confusing.

struct Foo2{
  this(T...)(T args){
    assert(0);
  }
}

void main(){
  auto a2=Foo2();//doesn't call assert(0) (ie this(T...) not
called)
}

 
 There is no "argument-less constructor" in D. "Struct()" is just
 shorthand for "Struct.init" (bar a few exceptional exceptions:
  disabled this() and static opCall).
 
 AFAIK, D decided to not have "default" constructors,

[...]

Note that this only applies to structs. Classes have default ctors.


T

-- 
Programming is not just an act of telling a computer what to do: it is
also an act of telling other programmers what you wished the computer to
do. Both are important, and the latter deserves care. -- Andrew Morton

"Gary Willoughby" <dev nomad.so> writes:

On Wednesday, 18 September 2013 at 05:28:41 UTC, Timothee Cour 
wrote:
 This may have been discussed before, but I'm not sure whether 
 this is a bug
 or not. In any case it's a bit confusing.

 struct Foo2{
   this(T...)(T args){
     assert(0);
   }
 }

 void main(){
   auto a2=Foo2();//doesn't call assert(0) (ie this(T...) not 
 called)
 }

You are not passing a value to the constructor. Use auto 
a2=Foo2(1);