On 4/26/2013 1:59 PM, Diggory wrote:
The actual value shouldn't be taken into
account when determining which overload to call, only the type should matter,
D has an interesting feature called VRP (value range propagation), where
implicit conversion very much depends on the value. For example:
ubyte b;
b = 100; // ok
b = 300; // error
This has been very successful in reducing the noise of having to insert casts
all over the place.
For:
enum e = 1;
then e is a value that is known to be one. Hence VRP applies, and it can be
implicitly cast to bool, ubyte, short, etc. For:
static e = 1;
the compiler cannot assume that e is always 1, hence e is treated as an int that
could hold any value. Hence, it cannot be implicitly cast to bool, ubyte, short,
etc.
> Ideally such an implicit conversion would only apply if it was the only
possible valid implicit conversion,
This was how D originally worked. However, it produced a list of foolish errors,
and a lot of complaints. The current scheme attempts to resolve ambiguities by
doing a "partial ordering" (described elsewhere in this thread). This has been
very successful.
To make use of overloading, there's no avoiding understanding this. A program
that breaks due to different overloadings of:
enum e = 1;
static x = 1;
is misusing overloading just like one that breaks on different overloads of:
enum e = 30000;
static x = 40000;
I.e.:
void foo(short) { ... back up my files ... }
void foo(long) { ... launch nuclear missiles ... }
is a bad program.
