On 11/03/2019 08:55 AM, Vinod K Chandran wrote:
> Hi all,
> I can do this in C++.
> #include <iostream>
> using namespace std ;
>
> #define end };
> #define log(x) cout << x << endl
> #define wait std::cin.get()
There is nothing that stops one from using the C++ preprocessor on any
text file. For example, you can do the following wherever GCC exists. If
there are the following lines in a D file:
#define XYZ 42
auto a = XYZ;
Then you can pass it through the preprocessor like this:
cpp foo.d
In fact, that's one of the tricks dpp uses to make C++ headers usable in
D code:
https://github.com/atilaneves/dpp
As you can see above, compile-time constants are defined with 'enum' in D:
enum XYZ = 42;
auto a = XYZ;
Beware though: Do not do that with arrays though, as every usage of an
'enum' array causes dynamic memory allocation at run time.
enum myConstants = [ 1, 2 ];
bool foo(int i) {
import std.algorithm : canFind;
return myConstants.canFind(i); // <-- DON'T DO THIS
}
In addition to the enum version of an array (which you may need to use
e.g. with 'static foreach') , also use a run-time initialized array:
// Use this e.g. for 'static foreach'
enum myConstants_enum = [ 1, 2 ];
// Use this for run-time code
immutable int[] myConstants;
shared static this() {
// This is the initialization of the immutable array:
myConstants = myConstants_enum;
}
bool foo(int i) {
import std.algorithm : canFind;
return myConstants.canFind(i); // <-- DO THIS
}
Even though I've known about this gotcha, this wisdom comes from
profiling my program by compiling with dmd's '-profile=gc' option. It
was pretty obvious in the generated 'profilegc.log' file that I was
causing such unnecessary memory allocations.
Ali
