On Friday, 26 July 2019 at 06:24:18 UTC, evilrat wrote:
On Friday, 26 July 2019 at 03:42:58 UTC, Andrey Zherikov wrote:
Is there a way to check whether some module, say "foo", is
available for import before doing "import foo"?
I did some really retarded utility like this in the past,
worked for me, but I can't say it is that well tested and there
might be a better way (after all it just assumes that template
instantiation failure can only mean there is no such module),
so in short template allowed to fail, and we check if it is
failed or not to test if desired module exists. Don't remember
if static is really necessary or you can just return directly.
bool isModuleAvailable(alias modName)() {
mixin("import " ~ modName ~ ";");
static if (__traits(compiles, mixin(modName).stringof))
return true;
else
return false;
}
// use like this
static if (__traits(compiles, isModuleAvailable!"mymod" ))
import mymod;
This works, thanks!
But when I try to wrap usage as a single call to something I get
slightly different result of import:
// mymod.d
module mymod;
void myfunc() { import std.stdio; writeln("myfunc"); }
// use1.d
static if (__traits(compiles, isModuleAvailable!"mymod" )) import
mymod;
pragma(msg,fullyQualifiedName!(myfunc)); // mymod.myfunc
pragma(msg,fullyQualifiedName!(mymod.myfunc)); // mymod.myfunc
// use2.d
mixin template my_import(alias modName)
{
static if (__traits(compiles, isModuleAvailable!modName ))
mixin("import " ~ modName ~ ";");
}
mixin my_import!"mymod";
pragma(msg,fullyQualifiedName!(myfunc)); // Error:
undefined identifier myfunc
pragma(msg,fullyQualifiedName!(mymod.myfunc)); // mymod.myfunc
Even without static if I get the same result:
mixin template my_import(alias modName)
{
mixin("import " ~ modName ~ ";");
}
mixin my_import!"mymod";
pragma(msg,fullyQualifiedName!(myfunc)); // Error:
undefined identifier myfunc
pragma(msg,fullyQualifiedName!(mymod.myfunc)); // mymod.myfunc
If I understood template mixin doc correctly this happens because
of "The declarations in a mixin are placed in a nested scope". So
is there a way to make two use cases above to work the same way,
i.e. "myfunc" to be available without "mymod." prefix?
