On Saturday, 12 September 2015 at 01:03:54 UTC, Prudence wrote:
On Thursday, 10 September 2015 at 18:02:36 UTC, Ali Çehreli
wrote:
On 09/10/2015 10:55 AM, Prudence wrote:
> How bout this:
>
> void myfunc(double delegate(int i, int z, float f)) {....}
>
>
> myfunc((int i, int z, float f) { return i*z*f; } }
>
> vs
>
> myfunc({ return i*z*f; }) // Names of parameters are
inferred from
> signature.
Considering other features of the language, that's pretty much
impossible in D. What if there is another i in scope:
int i;
myfunc({ return i*z*f; });
Now, should it call another overload of myfunc that takes (int
z, int f) because i is something else?
Should the compiler analyze the body of the code and decide
which symbols could be parameters? And then go through all
overloads of myfunc? etc.?
Ali
As I said, it could throw a warning or error. It, in some
sense, is already a a problem with nested blocks that hide
outside variables, is it not?
The compiler doesn't need to scan anything. It knows the which
parameters from the definition!
-> void myfunc(double delegate(int i, int z, float f)) <-
Compiler knows to use the names here as the default names in
for the parameters when.
when used:
myfunc({ return i*z*f; }); <- Oh, there are the names, we know
what they are because the signature is tells us. The compiler
does the following:
1. Sees we have a block without any parameters defined. i.e., a
lambda.
2. It looks up the signature of myfunc to find out what the
names are
3. It sees that they are i z and f
4. Now it knows and it effectively rewrites the code as
myfunc((i,z,f) { return i*z*f; });
Surely this is not difficult, 4 steps?
You're making your code more brittle for a small gain. The
suggestion makes parameter usage order important and the compiler
can't warn about my typos.
Consider:
myfunc({return "x:"~x~"y:"-y;}) getting changed to myfunc({return
"y:"~y~"x:"~x;});
Or the typo in
myfunc({return i*z+f*j;});
Lambdas are already very concise. This proposal doesn't give any
benefits outside of very simple lambdas. Such lambdas are already
so simple that they could use some standard functions instead
(like sum, to!T, and bind).
