• #ponce (11/11) Apr 23 2010 In C++ implicit constructors and conversion operators allow a user-defin...
• Robert Clipsham (21/32) Apr 23 2010 A combination of alias this and opAssign should work:
• Philippe Sigaud (8/45) Apr 23 2010 Could the compilation error comes from the compiler rewriting half f = 1...

#ponce <spam spam.spam> writes:

In C++ implicit constructors and conversion operators allow a user-defined type
to act quite like a builtin-type.

  struct half
  {
      half(float x);l
      inline operator float() const;
  }

allows to write:

  half x = 1.f;
  float f = x;

and this is especially useful for templates. 
I couldn't find a similar construct in D, is there any?

Robert Clipsham <robert octarineparrot.com> writes:

On 23/04/10 17:22, #ponce wrote:
 In C++ implicit constructors and conversion operators allow a user-defined
type to act quite like a builtin-type.

    struct half
    {
        half(float x);l
        inline operator float() const;
    }

 allows to write:

    half x = 1.f;
    float f = x;

 and this is especially useful for templates.
 I couldn't find a similar construct in D, is there any?

A combination of alias this and opAssign should work:
----
struct half
{
   float f;
   alias f this;
   half opAssign(float fl)
   {
     f = fl;
     return this;
   }
}

void main()
{
   half x;
   // For some reason I got a compilation error with half x = 1f;
   x = 1f;
   float f = x;
}
----

Philippe Sigaud <philippe.sigaud gmail.com> writes:

On Fri, Apr 23, 2010 at 18:46, Robert Clipsham <robert octarineparrot.com>wrote:

 On 23/04/10 17:22, #ponce wrote:

 In C++ implicit constructors and conversion operators allow a user-defined
 type to act quite like a builtin-type.

   struct half
   {
       half(float x);l
       inline operator float() const;
   }

 allows to write:

   half x = 1.f;
   float f = x;

 and this is especially useful for templates.
 I couldn't find a similar construct in D, is there any?

 A combination of alias this and opAssign should work:
 ----
 struct half
 {
  float f;
  alias f this;
  half opAssign(float fl)
  {
    f = fl;
    return this;
  }
 }

 void main()
 {
  half x;
  // For some reason I got a compilation error with half x = 1f;
  x = 1f;
  float f = x;
 }

Could the compilation error comes from the compiler rewriting half f = 1f;
into half f(1f); or somesuch and trying to call a constructor?
I'm tearing my hair due to errors/confusions between constructors and opCall
for structs.

Anyway, in your example, adding

this(float f) { this.f = f;}

is enough to get half f = 1f; to compile.