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digitalmars.D.learn - alias and mixin

reply "evilrat" <evilrat666 gmail.com> writes:
what the problem with this?

alias myint = mixin("int"); // <- basic type expected blah blah 
blah...

mixin alias unusable now, it blocks various cool templates and 
really frustrating(such things make D feels like some cheap 
limited language), is there any way to tell compiler explicitly 
use mixin result for aliasing like above?
Aug 31 2014
parent reply ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On Sun, 31 Aug 2014 11:26:47 +0000
evilrat via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
wrote:


 alias myint =3D mixin("int"); // <- basic type expected blah blah=20


  mixin("alias myint =3D "~"int"~";");
?
Aug 31 2014
parent reply "evilrat" <evilrat666 gmail.com> writes:
On Sunday, 31 August 2014 at 11:43:03 UTC, ketmar via 
Digitalmars-d-learn wrote:

 On Sun, 31 Aug 2014 11:26:47 +0000
 evilrat via Digitalmars-d-learn 
 <digitalmars-d-learn puremagic.com>
 wrote:


 alias myint = mixin("int"); // <- basic type expected blah blah


   mixin("alias myint = "~"int"~";");
 ?


wow, it works. i don't even think inverting it O_o
you saved my day, thanks.
Aug 31 2014
next sibling parent reply "Dicebot" <public dicebot.lv> writes:
On Sunday, 31 August 2014 at 12:01:43 UTC, evilrat wrote:

 On Sunday, 31 August 2014 at 11:43:03 UTC, ketmar via 
 Digitalmars-d-learn wrote:

 On Sun, 31 Aug 2014 11:26:47 +0000
 evilrat via Digitalmars-d-learn 
 <digitalmars-d-learn puremagic.com>
 wrote:


 alias myint = mixin("int"); // <- basic type expected blah 
 blah


  mixin("alias myint = "~"int"~";");
 ?


 wow, it works. i don't even think inverting it O_o
 you saved my day, thanks.


It is basically just an annoying grammar limitation that does not 
allow to use mixin / __traits as an identifier.
Aug 31 2014
parent reply Philippe Sigaud via Digitalmars-d-learn writes:
 It is basically just an annoying grammar limitation that does not allow to
 use mixin / __traits as an identifier.


The usual helper template:

```
    alias helper(alias a) = a;
```

helps for aliasing __traits and anonymous function templates (x =>
x+1), but I don't see an easy solution for mixin inside the current
language, apart from pushing the mixin outside.
Aug 31 2014
parent reply "Dicebot" <public dicebot.lv> writes:
On Sunday, 31 August 2014 at 14:46:00 UTC, Philippe Sigaud via 
Digitalmars-d-learn wrote:

 It is basically just an annoying grammar limitation that does 
 not allow to
 use mixin / __traits as an identifier.


 The usual helper template:

 ```
     alias helper(alias a) = a;
 ```

 helps for aliasing __traits and anonymous function templates (x 
 =>
 x+1), but I don't see an easy solution for mixin inside the 
 current
 language, apart from pushing the mixin outside.


I recommend slightly more generic form:

template Alias(T...)
     if (T.length == 1)
{
     alias Alias = T[0];
}

it is quite helpful in templated code to be able to alias 
_anything_

But yeah, no fun for mixins :(
Aug 31 2014
parent Philippe Sigaud via Digitalmars-d-learn writes:
 I recommend slightly more generic form:

 template Alias(T...)
     if (T.length == 1)
 {
     alias Alias = T[0];
 }

 it is quite helpful in templated code to be able to alias _anything_


That's what I use also, but didn't want another thread on the (T...)
if (T.length ==1) trick :)



 But yeah, no fun for mixins :(


Mainly, I slap them in my code, then slowly migrate them outwards (in
'head' position) until that compiles...
Aug 31 2014
prev sibling parent reply "evilrat" <evilrat666 gmail.com> writes:
On Sunday, 31 August 2014 at 12:01:43 UTC, evilrat wrote:

 On Sunday, 31 August 2014 at 11:43:03 UTC, ketmar via 
 Digitalmars-d-learn wrote:

 On Sun, 31 Aug 2014 11:26:47 +0000
 evilrat via Digitalmars-d-learn 
 <digitalmars-d-learn puremagic.com>
 wrote:


 alias myint = mixin("int"); // <- basic type expected blah 
 blah


  mixin("alias myint = "~"int"~";");
 ?


 wow, it works. i don't even think inverting it O_o
 you saved my day, thanks.


ugh... somewhat related to original problem, made simple template 
for quick check if type present or provide alternative.

now that is something i am not understand.

sorry for my stupidness :(

--- code
struct A {}
alias coolStruct = typeByName!("MyStruct", A);

// oops, looks like alias is set to template itself, though
// code completion(mono-d) shows it is correctly aliased to A
//
// error: template instance is used as a type
void doSomething(coolStruct cs)
{
  .. do something with struct ..
}

--- template itself
template typeByName(alias Name, Replace)
{
  static if ( __traits(compiles, (mixin(Name~`.sizeof`))) )
   mixin(`alias typeByName = ` ~ Name ~ `;`);
  else
   static if ( (is(Replace == class) || is(Replace == struct)) )
    alias typeByName = Replace;
}
Sep 01 2014
next sibling parent ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On Mon, 01 Sep 2014 10:57:41 +0000
evilrat via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
wrote:

here's some more ugly hackery for you:

    string makeAlias(string aliasName, string Name, alias Replace) ()
    {
      static if ( __traits(compiles, (mixin(Name~`.sizeof`))) )
        return `alias `~aliasName~` =3D ` ~ Name ~ `;`;
      static if ( (is(Replace =3D=3D class) || is(Replace =3D=3D struct)) )
        return `alias `~aliasName~` =3D ` ~ Replace.stringof ~ `;`;
      assert(0);
    }


    struct A {}
    mixin(makeAlias!("coolStruct", "MyStruct", A));

or:

    mixin template makeAlias(string aliasName, string Name, alias Replace)
    {
      static if ( __traits(compiles, (mixin(Name~`.sizeof`))) )
        mixin(`alias `~aliasName~` =3D ` ~ Name ~ `;`);
      static if ( (is(Replace =3D=3D class) || is(Replace =3D=3D struct)) )
        mixin(`alias `~aliasName~` =3D ` ~ Replace.stringof ~ `;`);
      else static assert(0);
    }


    struct A {}
    mixin makeAlias!("coolStruct", "MyStruct", A);
Sep 01 2014
prev sibling next sibling parent ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On Mon, 01 Sep 2014 10:57:41 +0000
evilrat via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
wrote:

and to check that ugly hackery:

    mixin template makeAlias(string aliasName, string Name, alias
    Replace) {
      static if ( __traits(compiles, (mixin(Name~`.sizeof`))) )
        mixin(`alias `~aliasName~` =3D ` ~ Name ~ `;`);
      static if ( (is(Replace =3D=3D class) || is(Replace =3D=3D struct)) )
        mixin(`alias `~aliasName~` =3D ` ~ Replace.stringof ~ `;`);
      else static assert(0);
    }


    struct A {}
    struct B {}
    struct C {}
    mixin makeAlias!("coolStruct", "MyStruct", A);
    mixin makeAlias!("coolStruct1", "B", C);

    void doSomething(coolStruct cs)
    {
      static if (!is(typeof(cs) =3D=3D A)) static assert(0);
      //.. do something with struct ..
    }

    void doSomething1(coolStruct1 cs)
    {
      static if (!is(typeof(cs) =3D=3D B)) static assert(0);
      //.. do something with struct ..
    }
Sep 01 2014
prev sibling parent reply ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On Mon, 01 Sep 2014 10:57:41 +0000
evilrat via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
wrote:

p.s. you should really read about D mixins and templates. they aren't
such intuitive sometimes, has their set of funny restrictions, and it
may be hard to 'guess the right way' sometimes.

but to be honest, i wasn't read any books and found alot of things by
experimenting, so it's not a dead-end way too. ;-)
Sep 01 2014
parent reply "evilrat" <evilrat666 gmail.com> writes:
On Monday, 1 September 2014 at 11:23:37 UTC, ketmar via 
Digitalmars-d-learn wrote:

 On Mon, 01 Sep 2014 10:57:41 +0000
 evilrat via Digitalmars-d-learn 
 <digitalmars-d-learn puremagic.com>
 wrote:

 p.s. you should really read about D mixins and templates. they 
 aren't
 such intuitive sometimes, has their set of funny restrictions, 
 and it
 may be hard to 'guess the right way' sometimes.

 but to be honest, i wasn't read any books and found alot of 
 things by
 experimenting, so it's not a dead-end way too. ;-)


thanks again, i also made tweaks to my original template to check 
for aliases and now it works too, means that error message was 
totally misleading.
btw i had read some articles about mixins and templates but still 
difference between template and mixin template is somewhat 
confusing.

and D states "intuitive is the way", yeah...
Sep 01 2014
parent ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On Mon, 01 Sep 2014 11:56:33 +0000
evilrat via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
wrote:


 and D states "intuitive is the way", yeah...


it's still way better than C++. ;-)
Sep 01 2014