constructing module level immutable variables at runtime?

[Danni Coy via Digitalmars-d]

I am trying to port a heavily multithreaded C++ application to D.

I have a lot of variables that are set once from a config file at
runtime and then never change.
It seems that something like the following would be a very clean design.

module config;

static this()
{
    num_triggers = to!int(getValueFromConfigFile());
}

private:
immutable(int) num_triggers = void;

Is there any reason that allowing this would be a bad idea?