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Shadonototra

While D is great, it also has some issues

- float default is NaN, why... just WHY!!!!!

- char default is 0xFF....

when you expect things to be just 0, it is a pain to deal with and to remember...

Also the standard library, while useful, i wish it would make use of allocators

They have ``std.experimental.allocator`` packages, for some reason it still is experimental..

There is no tagged union.. you have to import a package for it ``std.sumtype``.. wich is bad when all other languages have built in support for that

Walter if you read this, please! union are useful, but lack of tagged union mean potential bugs in your union when you pick the wrong value...

Proposal for you:

  enum MyTag { A, B, C}

  union MyTaggedUnion: MyTag
  {
      DataA A,
      DataB B,
      DataC C
  }

  struct DataA{}
  struct DataB{}
  struct DataC{}

  auto tgu = MyTaggedUnion.B;
  switch (tgu)
  {
   case A:
   tgu. /* implicit DataA */
   break;
   // need to implement every tags, or error
  }

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> float default is NaN, why... just WHY!!!!!

> char default is 0xFF....

Invalid values, perhaps? Other than making initialization mandatory, this seems like a reasonable way of catching them. For integer types it's not really possible because all their values are valid.

I grew to agree, but that doesn't mean that's not annoying.. i'm nitpicking

Why is your proposal better than this:

  import std.sumtype;
  
  void main(){
   struct A { int a; }
   struct B { string b; }
   struct C { bool c; }
   
   alias TaggedUnion = SumType!(A, B, C);
   
   auto tgu = TaggedUnion(B("hi"));
   int i = tgu.match!(
    (A a) => a.a,
    (B b) => b.b.length,
    (C c) => c.c * 5
   );
   assert(i == 2);
  }

If you miss out a `match` handler for any of A, B, C you get a compile-time error. Or you can use a generic handler which will be instantiated for any type not explicitly handled. https://dlang.org/phobos/std_sumtype.html

I'd take a language that have built in support for tagged union over having to import a module and rely on templates

I know of sumtype, and i think it is a mistake for D to rely on this for such important language feature

I'm not a language dev, so i can't do much to help, using switch/union/enum is more natural, is cleaner, and is easier to add support for IDEs, everyone on the same page

That's in areas like this where the language falls short, and i can see people instead choosing alternatives

https://github.com/dlang/phobos/blob/master/std/sumtype.d

a mess of templates and imports to std.traits

using this will make your compile speed tank.. another reason to avoid

it's very sad that people recommend this instead of asking for built-in version, makes me sometimes reconsider my choice to use the language

if they expect language improvements to be templates, what atrocity will be added next?

this is on the same level as std::bool from C++

https://forum.dlang.org/post/bkgvdewkjwthmlfemnjm@forum.dlan...

> The good news is, I have not put a lot of effort so far into micro-optimizing the compile-time performance of match, so there is almost certainly room for improvement.

it is shame that it ended up in the standard library

once Walter will be gone, i will have no faith in the language anymore

bool is a built-in type in C++...

> float default is NaN, why... just WHY!!!!!

All operations that are fed NaN as an operand produce a NaN result. This makes it very obvious when the initialization of a float has been neglected. Defaulting to 0.0 means uninitialization bugs are nearly impossible to detect.

> char default is 0xFF....

Same thing. It's intended to flush out uninitialization bugs.

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