F i L:
So basically, it's for debugging?
To avoid bugs it's useful for all variables to be initialized
before use (maybe with an explicit annotation for the uncommon
cases where you want to use uninitialized memory, like:
http://research.swtch.com/sparse ). Having a variable not
initialized is a common source of bugs.
C# solves this requiring explicit initialization all variables
before use. Walter doesn't believe that flow analysis is flexible
enough in a system language like D (or he doesn't want to
implement it) so he has not used this idea in D.
So D uses a different worse strategy, it initializes the
variables to something unusable, so if you try to use them, your
program fails clearly.
The idea of setting the variables to something useful, like
setting initialized chars to 'a' and floating point values to 0.0
looks handy, but on the long run it's not an improvement. You
sometimes don't initialize a char variable because you are fine
for it to be 'a', and some other times you don't set it just
because you forget to initialize it. The compiler can't tell
apart the two cases, and this is may be a bug in your code.
In practice I think having FP variables initialized to NaN has
not avoided me significant bugs in the last years. On the other
hand I have ported some C code that uses global floating point
arrays/variables to D, and I have had to remove some bugs caused
by the assumption in the C code that those global FP variables
are initialized to zero, that's false in D.
Another source of troubles is large fixed-sized FP global arrays,
that inflate the binary a *lot*. You have to remember to
initialize them to zero explicitly:
double[100_000] foo; // bad, inflates binary.
double[100_000] bar = 0.0; // good.
void main() {}
In D I'd like the solution used by C# + an annotation to not
initialize a variable or array.
Bye,
bearophile
