Re: Is there a -Dmacro like option for D compilers?

[ryuukk_ via Digitalmars-d-learn]

I just remembered you can do something like this!


```
import std.stdio;

enum FEATURE_A_AVAILABLE()
{
version(FEATURE_A) return true;
else return false;
}

void main()
{
static if (!FEATURE_A_AVAILABLE)
{
writeln("feature A not available");
}

}
```

It's evaluated at compile time, so it's branchless!

Re: Is there a -Dmacro like option for D compilers?

[ryuukk_ via Digitalmars-d-learn]

On Monday, 27 March 2023 at 22:22:26 UTC, Jeremy wrote:
Is there a way I can define a manifest constant from the 
compiler command-line, like the -Dmacro option for C compilers?


You can do this way:


```
dmd -version=FEATURE_A
```

```D

import std.stdio;

void main()
{

version(FEATURE_A)
{
writeln("feature A enabled");
}

}

```

Unfortunatly there is not #ifndef, so in case you want to make 
sure FEATURE_A is not there you'll have to do:


```D

import std.stdio;

void main()
{

version(FEATURE_A)
{}
else
{
writeln("feature A not available");
}

}

```


or

```D

import std.stdio;


version(FEATURE_A)
{
enum FEATURE_A_AVAILABLE = true;
}
else
{
enum FEATURE_A_AVAILABLE = false;
}

void main()
{
static if (!FEATURE_A_AVAILABLE)
{
writeln("feature A not available");
}

}

```


For some reason they force us to be overly verbose

Or it's possible to do it, but i don't know much more than this 
about ``-version``



(if you use ldc compiler, it's ``-d-version=``)

Is there a -Dmacro like option for D compilers?

[Jeremy via Digitalmars-d-learn]

Is there a way I can define a manifest constant from the compiler 
command-line, like the -Dmacro option for C compilers?