assume the files:

app.d

> void main() {
>   import myModule : foo;
>    writeln(foo(...));
>
> }

myModule.d

module myModule;
> int foo(int n) { .... }

the following fail:

> dmd -run app.d mymodule.d

give error like this:

> Error: module `myModule` is in file 'myModule.d' which cannot be read

but this doesn't fail:

> dmd app.d mymodule.d && app

Why does -run fail here? I thought it was a shorthand to this batch:

> dmd app.d mymodule.d
> app.exe
> del app.exe

On Wednesday, 14 March 2018 at 14:44:24 UTC, Marc wrote:
> Why does -run fail here? I thought it was a shorthand to this batch:

Check the help text:

$ dmd -h
  dmd [<option>...] -run <file> [<arg>...]
  <arg>            Argument to pass when running the resulting program

Notice that there's only one file there. Everything after it is passed as args to the resulting program. So dmd -run cannot support multiple D files.

Though, with the new `-i` option you might be able to get it to infer modules.

dmd -i -run file_with_main.d args_to_main.......

and if it can locate the other modules automatically it should bring them in there.

On Wednesday, 14 March 2018 at 14:44:24 UTC, Marc wrote:
> assume the files:
>
> app.d
>
>> void main() {
>>   import myModule : foo;
>>    writeln(foo(...));
>>
>> }
>
> myModule.d
>
> module myModule;
>> int foo(int n) { .... }
>
> the following fail:
>
>> dmd -run app.d mymodule.d
>
> give error like this:
>
>> Error: module `myModule` is in file 'myModule.d' which cannot be read
>
> but this doesn't fail:
>
>> dmd app.d mymodule.d && app
>
> Why does -run fail here? I thought it was a shorthand to this batch:
>
>> dmd app.d mymodule.d
>> app.exe
>> del app.exe

Not even that dmd mymodule.d -run app.d works and dmd -i -run app.d works too.

However, at the moment -run needs to be the last parameter. That's a more or less arbitrary restriction.
And no one has lifted it (yet).
Though there's a bit of work on that front:

https://github.com/dlang/dmd/pull/7927

The main problem is that the arguments after -run module are passed to the program and thus -run can be ambiguous.