www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - static assert(version(x)) ?

reply =?iso-8859-1?Q?Robert_M._M=FCnch?= <robert.muench saphirion.com> writes:
How can I write something like this to check if any of a set of 
specific versions is used?

static assert(!(version(a) | version(b) | version(c)):

The problem is that I can use version(a) like a test, and the symbol a 
is not accessbile from assert (different, non-accessible namespace).

-- 
Robert M. Münch
http://www.saphirion.com
smarter | better | faster
Nov 26 2019
next sibling parent Andrea Fontana <nospam example.com> writes:
On Tuesday, 26 November 2019 at 10:24:00 UTC, Robert M. Münch 
wrote:

 How can I write something like this to check if any of a set of 
 specific versions is used?

 static assert(!(version(a) | version(b) | version(c)):

 The problem is that I can use version(a) like a test, and the 
 symbol a is not accessbile from assert (different, 
 non-accessible namespace).


version(A) { enum isA = true; } else { enum isA = false; }
version(B) { enum isB = true; } else { enum isB = false; }

static assert(!(isA || isB));
Nov 26 2019
prev sibling next sibling parent reply S.G <S.G sdfsdfsfsdfsdf.gs> writes:
On Tuesday, 26 November 2019 at 10:24:00 UTC, Robert M. Münch 
wrote:

 How can I write something like this to check if any of a set of 
 specific versions is used?

 static assert(!(version(a) | version(b) | version(c)):

 The problem is that I can use version(a) like a test, and the 
 symbol a is not accessbile from assert (different, 
 non-accessible namespace).


BTW D language designers are against boolean eval of version.
It's not a technical restriction, it's just that they don't want 
this to work.
Nov 26 2019
parent reply Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:
On Tuesday, November 26, 2019 4:29:18 AM MST S.G via Digitalmars-d-learn 
wrote:

 On Tuesday, 26 November 2019 at 10:24:00 UTC, Robert M. Münch

 wrote:

 How can I write something like this to check if any of a set of
 specific versions is used?

 static assert(!(version(a) | version(b) | version(c)):

 The problem is that I can use version(a) like a test, and the
 symbol a is not accessbile from assert (different,
 non-accessible namespace).


 BTW D language designers are against boolean eval of version.
 It's not a technical restriction, it's just that they don't want
 this to work.


Basically, Walter considers it to be a prime source of bugs in C/C++ code.
druntime, Phobos, etc. consistently do stuff like

version(Posix)
{
}
else version(Windows)
{
}
else
    static assert(false, "platform unsupported);

when it needs code to differ depending on platform or architecture or
whatever. And if that means duplicating some code in each version block,
then it means duplicating some code in each version block. static if can be
used instead of version blocks to get boolean conditions, and local version
identifiers can be defined which combine some set of version identifiers,
but such practices are discouraged for D programmers in general, and they're
basically forbidden in official source code. The only case I'm aware of
where anything like that is used in druntime or Phobos is for darwin stuff,
since darwin isn't a predefined identifier.

- Jonathan M Davis
Nov 26 2019
parent reply Johan Engelen <j j.nl> writes:
On Tuesday, 26 November 2019 at 12:53:02 UTC, Jonathan M Davis 
wrote:

 On Tuesday, November 26, 2019 4:29:18 AM MST S.G via 
 Digitalmars-d-learn wrote:

 On Tuesday, 26 November 2019 at 10:24:00 UTC, Robert M. Münch

 wrote:

 How can I write something like this to check if any of a set 
 of specific versions is used?

 static assert(!(version(a) | version(b) | version(c)):

 The problem is that I can use version(a) like a test, and the
 symbol a is not accessbile from assert (different,
 non-accessible namespace).


 BTW D language designers are against boolean eval of version. 
 It's not a technical restriction, it's just that they don't 
 want this to work.


 ...
 static if can be used instead of version blocks to get boolean 
 conditions, and local version identifiers can be defined which 
 combine some set of version identifiers, but such practices are 
 discouraged for D programmers in general, and they're basically 
 forbidden in official source code. The only case I'm aware of 
 where anything like that is used in druntime or Phobos is for 
 darwin stuff, since darwin isn't a predefined identifier.


`xversion` is a simple and effective and useful tool, used in dmd 
source:
https://github.com/dlang/dmd/blob/53b533dc7fc5da604e7ebf457734766b4e96d900/src/dmd/globals.d#L21-L35

```
template xversion(string s)
{
     enum xversion = mixin(`{ version (` ~ s ~ `) return true; 
else return false; }`)();
}

enum version_a = xversion!`a`;
```

-Johan
Nov 27 2019
parent =?iso-8859-1?Q?Robert_M._M=FCnch?= <robert.muench saphirion.com> writes:
On 2019-11-27 18:50:07 +0000, Johan Engelen said:


 On Tuesday, 26 November 2019 at 12:53:02 UTC, Jonathan M Davis wrote:

 On Tuesday, November 26, 2019 4:29:18 AM MST S.G via Digitalmars-d-learn wrote:

 On Tuesday, 26 November 2019 at 10:24:00 UTC, Robert M. Münch
 
 wrote:

 How can I write something like this to check if any of a set of 
 specific versions is used?
 
 static assert(!(version(a) | version(b) | version(c)):
 
 The problem is that I can use version(a) like a test, and the
 symbol a is not accessbile from assert (different,
 non-accessible namespace).


 
 BTW D language designers are against boolean eval of version. It's not 
 a technical restriction, it's just that they don't want this to work.


 
 ...
 static if can be used instead of version blocks to get boolean 
 conditions, and local version identifiers can be defined which combine 
 some set of version identifiers, but such practices are discouraged for 
 D programmers in general, and they're basically forbidden in official 
 source code. The only case I'm aware of where anything like that is 
 used in druntime or Phobos is for darwin stuff, since darwin isn't a 
 predefined identifier.


 
 `xversion` is a simple and effective and useful tool, used in dmd source:


That's pretty neat... going to try this.

-- 
Robert M. Münch
http://www.saphirion.com
smarter | better | faster
Nov 28 2019
prev sibling parent Dennis <dkorpel gmail.com> writes:
On Tuesday, 26 November 2019 at 10:24:00 UTC, Robert M. Münch 
wrote:

 How can I write something like this to check if any of a set of 
 specific versions is used?


```
version(a) {}
else version(b) {}
else version(c) {}
else {
    static assert(0, "only versions a, b and c are supported");
}
```

```
version(a) version = supported;
version(b) version = supported;
version(c) version = supported;
version(supported) {
     // good to go
} else {
     static assert(0, "not a supported version");
}
```


 static assert(!(version(a) | version(b) | version(c)):


That seems to be the opposite of what you describe.
If you want that, then:
```
version(a) static assert(0, "version a not supported");
version(b) static assert(0, "version b not supported");
version(c) static assert(0, "version c not supported");
```
Nov 26 2019