On Monday, 6 June 2016 at 21:57:20 UTC, Pie? wrote:
On Monday, 6 June 2016 at 21:31:32 UTC, Alex Parrill wrote:
On Monday, 6 June 2016 at 17:31:52 UTC, Pie? wrote:
Is it possible to parse a file at compile time without
embedding it into the binary?
I have a sort of "configuration" file that defines how to
create some objects. I'd like to be able to read how to
create them but not have that config file stick around in the
binary.
e.g., (simple contrived example follows)
Config.txt
x, my1
y, my1
z, my2
class my1 { }
class my2 { }
void parseConfig(A)
{
....
}
void main()
{
parseConfig('Config.txt') // Effectively creates a mixin
that mixes in auto x = new my1; auto y = new my1; auto z =
new my2;
}
If parseConfig uses import('Config.txt') then config.txt will
end up in the binary which I do not want. It would be easier
to be able to use import and strip it out later if possible.
Config.txt may contain secure information, which is why is
doesn't belong in the binary.
Most compilers, I believe, will not embed a string if it is
not used anywhere at runtime. DMD might not though, I'm not
sure.
This doesn't seem to be the case. In a release build, even
though I never "use" the string, it is embedded. I guess this
is due to not using enum but enum seems to be much harder to
work with if not impossible.
But reading sensitive data at compile-time strikes me as
dangerous, depending on your use case. If you are reading
sensitive information at compile time, you are presumably
going to include that information in your binary (otherwise
why would you read it?), and your binary is not secure.
Not necessarily, You chased that rabbit quite far! The data
your reading could contain sensitive information only used at
compile time and not meant to embed. For example, the file
could contain login and password to an SQL database that you
then connect, at compile time and retrieve that information the
disregard the password(it is not needed at run time).
This is definitely possible, but it can depend on your compiler.
If you use an enum, it'll be treated as a compile-time constant -
so if you never store it anywhere (i.e. enum File =
import('file.txt'); string file = File; is a no-no at global
scope), you should be fine.
If you do find yourself in the precarious situation of storing
the data, then it's up to your compiler to detect that there are
no runtime references to the data and elide it. LDC and GDC most
likely do this, but I doubt DMD would.
For safety, you should try and reformulate your code in terms of
enums and local variables; this *should* work with DMD, but it's
possible it's not smart enough to catch onto the fact that the
function is never used at run-time (and therefore does not need
to be included in the executable).
