On Monday, 30 April 2018 at 21:56:23 UTC, H. S. Teoh wrote:
On Mon, Apr 30, 2018 at 09:31:48PM +0000, Giles Bathgate via
Digitalmars-d wrote: [...]
[...]
T
On Monday, 30 April 2018 at 21:56:23 UTC, H. S. Teoh wrote:
[...]
Appart from the good points Teoh has made, imagine you would have
to statically type in for loops:
foreach (i; items)
writefln("%s", i);
And, yeah, chainig would indeed be a PIA:
auto items = myRange.filter!(a => a.length);
Most of the time you don't really care about the exact type, only
at the end of the block (e.g. it should be `string[]`). And the
compiler always tells you about the types, e.g. something like
"cannot implicitly convert `words` of type MapResult to
string[]". And then, _at the end_, you can use something like
items.array;
to get `string[]`.
I think the problem is not `auto`, the problem is thinking in old
ways. If you think old-style Java where you declare loads of
statically typed class variables at the beginning, then you're in
trouble. But in order to use `auto`, you have to use a different
approach.
Java:
String name;
String address;
int uiid;
...
String getName()
{
return name;
}
[...]
In D, you are more likely to use home made structs / ranges /
tuples as return types that all have the same properties, so auto
makes more sense (incomplete code):
auto byUser(R)(R entries)
{
struct User
{
private
{
R entries;
}
this(R entries)
{
this.entries = entries;
}
@property bool empty() { return range empty? (true|false) }
@property void popFront()
{
// e.g.
entries = entries[1..$];
}
@property auto front()
{
return whatever; // e.g. struct UserInfo { string name;
size_t uuid; }
}
}
return User(entries);
}
The struct `User` can perform whatever is necessary, it can be
changed, even renamed but the return type will always conform to
the range interface: empty, popFront, front, so the caller can be
sure s/he can use it as a range. Also, the type of `entries` can
change, but the code will still work. No need to redefine all the
variables as a different type. Now
auto users = entries.byUser();
can be whatever and you can perform other range based algorithms
[1]
auto herberts = entries.byUser.filter!(a => a.name ==
'Herbert')...etc.etc.
Imagine having to use handwritten static typing for that!
[1] https://tour.dlang.org/tour/en/gems/range-algorithms
