On 2011-03-24 14:05, spir wrote:
On 03/24/2011 12:07 PM, bearophile wrote:
I have discussed this is little problem about three years ago; in the
meantime the situation is changed (rdmd has appeared, DMD has grown
the -deps switch, etc).
I have a little module named "modu":
module modu;
import std.stdio;
int foo() {
return 0;
}
int main() {
writeln("modu.main");
return 1;
}
I create a second module named "somemodule", and import just the foo()
function from mod:
module somemodule;
import std.stdio;
import modu: foo;
int main() {
writeln("somemodule.main");
return foo();
}
Now if I compile somemodule normally, with:
rdmd somemodule.d
I receive an error like:
OPTLINK (R) for Win32 Release 8.00.12
Copyright (C) Digital Mars 1989-2010 All rights reserved.
http://www.digitalmars.com/ctg/optlink.html
... Offset 00137H Record Type 00C3
Error 1: Previous Definition Different : __Dmain
--- errorlevel 1
To avoid this problem in Python there is a common idiom:
if __name__ == '__main__':
# main code here...
This idiom allows to define and run a "main" only for the main module.
Currently in D there is no notion of "main module", but I see a simple
way to avoid this problem in D too, defining a new standard version
name that tools like rdmd, bud, etc define for just the first module
(like for the only module name given to rdmd), and don't define for
all other modules found and compiled recursively:
module mod;
int foo() {
return 0;
}
version (main_module) int main() {
return 1;
}
The usage of main_module is optional.
I like to keep a main() in most modules, even the ones that are
usually not supposed to be the main modules of a program, because I
put in their main() some demo code that shows what this module does
(and a main is useful to run unittests too, rdmd has the --main switch
for this). Most of my Python modules have such demo main code, that
runs only if you run them as main modules.
I support finding a solution for this issue. Very annoying esp. during
development since running unittests on a module, or set of modules,
requires a main() func. But the module(s) one needs to run the unittests
of are not always (conceptualy) the main app's module; there may even be
none, if it's a lib. So, we need stupidly need to add a fake & empty
main() func -- that will later generate linking error when building the
whole app ;-)
But I do not like your solution, which i find uselessly complicated. In
order of preference:
* the linker automatically adds an empty main() to the first module if
needed
* allow empty main() in every module, more than one beeing just ignored
* your solution
Denis
Doesn't rdmd have an option to add a main function?
--
/Jacob Carlborg
