On Saturday, 29 June 2013 at 01:49:01 UTC, JS wrote:
On Saturday, 29 June 2013 at 01:31:13 UTC, Walter Bright wrote:
On 6/28/2013 5:00 PM, JS wrote:
Is variant useful? If not then you have a point. I'm not
proposing anything that
variant can't already do except add compile time performance.
I do not think the
complexity is much more than what is already done.
D already checks for time mismatch. With such a variant or
auto the check simply
is more intelligent.
e.g.,
auto x; // x's type is undefined or possibly variant.
x = 3; // x's type is set temporarily to an int
...
x = 3.0; // ****
at **** we have several possibilities.
1. Throw an error, this makes auto more useful and avoids
many pitfalls.
2. Set x's type to a variant. [possibly goto 3 if castable
to new type]
3. Set x's type to a double.
Both 2 and 3 require an extra pass to convert the code
because it uses forward
inference.
auto looks only at the immediate assignment expression to
determine the type. I
am talking about generalizing it to look in the scope with
possible fallback to
a variant type with optional warning, an error, or type
enlargement.
Again, I need a compelling use case. It's not enough to say
it's the same as variant, and it's not enough to say it can be
implemented.
A compelling use case would be a pattern that is commonplace,
and for which the workarounds are ugly, unsafe, error prone,
unportable, etc.
What was the use case for auto that got in into the language?
A quick look at any heavily templated c++ (pre c++11) is all you
need to justify it.
auto cuts code clutter by huge amounts all over the place.
