Re: how to test (at compilation-time) for existence of an already-declared object ?

[someone via Digitalmars-d-learn]

On Saturday, 24 July 2021 at 01:44:11 UTC, Adam D Ruppe wrote:

On Saturday, 24 July 2021 at 01:29:26 UTC, someone wrote:

Suppose I have a module with the following:



static if(is(classTickerCustomNYSE))
   // it was a valid type
else
  // it was not a valid type


can use that to test. you can also mix in the name


static if(is(mixin("class name here"))) {}



There's similar tricks for testing for imports and such too but 
i recommend here you import the module first then can test it.


is() ... faaan-tas-tic :)

I completely forgot about the is operator and went looking all 
over the place for something like that.


Man ... leaving templates aside for a moment, conditional 
compilation alongside mixin is pretty powerful in D ! I can't 
believe how flexible code I am writing right now; and I am only a 
beginner ...


Thanks for the tip Adam !

Re: how to test (at compilation-time) for existence of an already-declared object ?

[Adam D Ruppe via Digitalmars-d-learn]

On Saturday, 24 July 2021 at 01:29:26 UTC, someone wrote:

Suppose I have a module with the following:



static if(is(classTickerCustomNYSE))
   // it was a valid type
else
  // it was not a valid type


can use that to test. you can also mix in the name


static if(is(mixin("class name here"))) {}



There's similar tricks for testing for imports and such too but i 
recommend here you import the module first then can test it.

how to test (at compilation-time) for existence of an already-declared object ?

[someone via Digitalmars-d-learn]

Suppose I have a module with the following:

```d
public class classTickerCustomNYSE : classTickerCommon { ... }
public class classTickerCustomNASDAQ : classTickerCommon { ... }
```

... and given that I also have the following in the same module:

```d
public enum structureExchanges = [
   r"NYSE"d   : structureExchange(r"NYSE"d, r"New York Stock 
Exchange"d, r"USD"d, r"usa"d, r"New York"d, r"EST"d),
   r"NASDAQ"d : structureExchange(r"NASDAQ"d, r"National 
Association of Securities Dealers Automated Quotations"d, 
r"USD"d, r"usa"d, r"New York"d, r"EST"d),
   r"LSE"d: structureExchange(r"LSE"d, r"London Stock 
Exchange"d, r"GBP"d, r"gbr"d, r"London"d, r"UTC"d),
   r"XETRA"d  : structureExchange(r"XETRA"d, r"Deutsche Börse"d, 
r"EUR"d, r"deu"d, r"Frankfurt am Main"d, r"CET"d),
   r"B3"d : structureExchange(r"B3"d, r"B3 formerly Bolsa de 
Valores de São Paulo (aka BOVESPA)"d, r"BRL"d, r"bra"d, r"São 
Paulo"d, r"BRT"d),
   r"BCBA"d   : structureExchange(r"BCBA"d, r"Bolsa de Comercio 
de Buenos Aires"d, r"ARS"d, r"arg"d, r"Buenos Aires"d, r"ART"d)

   ];

public struct structureExchange { /// solely‐intended to help 
build code at compilation‐time; for client‐code classExchanges 
should be used instead


   public dstring ID;
   public dstring name;
   public dstring currencyID;
   public typeLocation location;

   @safe this(
  const dstring lstrExchangeID,
  const dstring lstrExchangeName,
  const dstring lstrCurrencyID,
  const dstring lstrCountryID,
  const dstring lstrCity,
  const dstring lstrTZ
  ) {

  ID = lstrExchangeID;
  name = lstrExchangeName;

  currencyID = lstrCurrencyID;

  location = typeLocation(
 lstrCountryID,
 lstrCity,
 lstrTZ)
 ;

   }

}
```

... at compilation-time I can do things like:

```d
static foreach (structureExchange sudtExchange; 
structureExchanges) { /// assume the following code as a template 
to build new classTickerCustom{ExchangeID} classes


   mixin(format!

  ` /// code chunk

  final public class classTickerCustom%1$s : 
classTickerCommon {


  ...

  }

  `(sudtExchange.ID) /// code chunk

   ); /// mixin ending

}
```

... now, question is: how can I check, within the static foreach 
code, whether a class is already-implemented or not; eg:


```d

static foreach (structureExchange sudtExchange; 
structureExchanges) {


   if (! ? == r"classTickerCustom"d ~ sudtExchange.ID) {

  /// class is not implemented yet: do whatever here ...

   }

}
```

... my first thought was traits 
(https://dlang.org/spec/traits.html) but I don't see anything 
useful there; there is getMember() but the example is for 
already-declared objects within the module, and not the module 
itself.