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digitalmars.D.learn - How do you declare manifest constants?

reply Andrey Zherikov <andrey.zherikov gmail.com> writes:
I want to embed some info from build system - version info, for 
example. I can easily do this with C++ compiler by 
`-DVERSION="1.2.3"` but there is no such an option in dmd. So I'm 
wondering how do people workaround this?
I see only one way: generate a file and add it to the build (file 
might be `.d` source or something included by import expression).
Nov 04 2021
parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On 11/4/21 12:43 PM, Andrey Zherikov wrote:

 I want to embed some info from build system - version info, for example. 
 I can easily do this with C++ compiler by `-DVERSION="1.2.3"` but there 
 is no such an option in dmd. So I'm wondering how do people workaround 
 this?
 I see only one way: generate a file and add it to the build (file might 
 be `.d` source or something included by import expression).


D doesn't have any equivalent for this. The closest you can get is to 
turn on `version` identifiers.

There is also a quirky `-version=123` which is IMO, a completely useless 
feature.

Your best bet is to do what you are doing -- generate a d file, and then 
include it.

Note, there is at least one dub package which does this for you: 
https://code.dlang.org/packages/gen-package-version

I use it in my build and it works OK. You just have to remember to 
attribute your tag in git.

-Steve
Nov 04 2021
parent reply Andrey Zherikov <andrey.zherikov gmail.com> writes:
On Thursday, 4 November 2021 at 17:09:31 UTC, Steven 
Schveighoffer wrote:

 D doesn't have any equivalent for this.


Is it possible to add this feature having `-C VERSION="1.2.3"` 
(`-D` is already used) to be equal to `enum VERSION="1.2.3"` in 
global namespace?


 The closest you can get is to turn on `version` identifiers.

 There is also a quirky `-version=123` which is IMO, a 
 completely useless feature.


I agree - this is useless. `-version myversion=123` would be much 
more useful.


 Note, there is at least one dub package which does this for 
 you: https://code.dlang.org/packages/gen-package-version


Unfortunately git/hg tags is not the only possible source of 
manifest constants.
Nov 04 2021
parent reply "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
On Thu, Nov 04, 2021 at 05:24:44PM +0000, Andrey Zherikov via
Digitalmars-d-learn wrote:

 On Thursday, 4 November 2021 at 17:09:31 UTC, Steven Schveighoffer wrote:

 D doesn't have any equivalent for this.


 
 Is it possible to add this feature having `-C VERSION="1.2.3"` (`-D`
 is already used) to be equal to `enum VERSION="1.2.3"` in global
 namespace?
 

 The closest you can get is to turn on `version` identifiers.
 
 There is also a quirky `-version=123` which is IMO, a completely
 useless feature.


 
 I agree - this is useless. `-version myversion=123` would be much more
 useful.


Here's a hack that uses dmd's stdin feature to inject D code into a
compile command:

	// main.d
	import __stdin : myversion;
	void main() {
		import std;
		writeln(myversion);
	}

Compile command:
	echo 'enum myversion = "1.2.3";' | dmd - -run main.d

Output:
	1.2.3

You can change the version number just by changing the echo command. And
of course, it doesn't have to be a string, it can be any valid D type,
and obviously you can declare more than one variable that can then be
read by importing from __stdin.


T

-- 
Don't throw out the baby with the bathwater. Use your hands...
Nov 04 2021
parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 11/4/21 10:36 AM, H. S. Teoh wrote:


 	import __stdin : myversion;


Where can we learn more of that magic? :)

Ali
Nov 04 2021
parent "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
On Thu, Nov 04, 2021 at 01:17:02PM -0700, Ali Çehreli via Digitalmars-d-learn
wrote:

 On 11/4/21 10:36 AM, H. S. Teoh wrote:
 

 	import __stdin : myversion;


 
 Where can we learn more of that magic? :)


[...]

I kinda cheated, because I was the one who implemented dmd's stdin
feature, so I knew that dmd implicitly creates a specially-named module
to contain the code read from stdin.  I had actually forgotten what the
name of this module was, but that was no problem since it was easily
found by:

	echo 'pragma(msg, __MODULE__);' | dmd -c -

which revealed the module name to be `__stdin`.

Next, thanks to D's module system, is the realization that you could
import this implicit module from somewhere else and pull symbols from
it.  From there, the everything else followed. :-)


T

-- 
There is no gravity. The earth sucks.
Nov 04 2021