Re: Compile time foreach with switch
On Friday, 21 April 2017 at 19:17:32 UTC, Adam D. Ruppe wrote:
On Friday, 21 April 2017 at 19:09:25 UTC, Johan Fjeldtvedt
wrote:
void foo(string s) {
enum es = tuple("a", "b", "c");
switch (s) {
foreach (e; es) {
case e:
writeln("matched ", e);
break;
}
Let me remove some surrounding stuff and ask you what happens:
foreach (e; es) {
if(s == c) {
writeln("matched ", e);
break;
}
}
What does that break do?
Then realize that it does exactly the same thing when it is
inside a switch... it always breaks the innermost thing, which
happens to be this loop. (note that cases are not `breaked`,
the switch is.)
*facepalm* Of course! Thanks.
Compile time foreach with switch
I was a bit surprised to find out
(https://forum.dlang.org/post/csiwyetjkttlxxnwn...@forum.dlang.org) that compile time foreach-loops can be used inside switch-statements. I tried the following:
import std.stdio;
import std.typecons;
void foo(string s) {
enum es = tuple("a", "b", "c");
switch (s) {
foreach (e; es) {
case e:
writeln("matched ", e);
break;
}
default:
writeln("no match");
break;
}
}
void main() {
foo("a");
}
However, this prints both "matched a" and "no match". It seems
like either the break or the default: label is ignored. In this
example I could have used return of course, but is this behavior
correct?
Re: Forwarding calls to objects of another type
On Tuesday, 11 April 2017 at 02:01:19 UTC, Nicholas Wilson wrote: On Monday, 10 April 2017 at 21:27:34 UTC, Basile B. wrote: 2) This is about the reduce templates. As I've commented, I can't use a template lambda with reduce, but I can use a lambda taking ints as arguments. Why is this? The error message I get when using the template lambda is: "template instance reduce!((a, b) => a + b) cannot use local '__lambda1' as parameter to non-global template reduce(alias fun)()" No idea for this. The use of the global identity template will fix this: see https://blog.thecybershadow.net/2015/04/28/the-amazing-template-that-does-nothing/ Thanks, that did work. I think I understand the point about UFCS lookup rules, but it still seems strange (it was at least surprising) that I couldn't use the template (a, b) => a + b in place of (int a, int b) => a + b.
Re: Forwarding calls to objects of another type
On Monday, 10 April 2017 at 21:27:34 UTC, Basile B. wrote: On Monday, 10 April 2017 at 21:04:10 UTC, Johan Fjeldtvedt wrote: [...] One way: [...] Thanks for the reply. The traits way of doing it seems to be what I want. :) [...] [...]
Forwarding calls to objects of another type
I have a couple of questions related to the following code: https://gist.github.com/Jaffe-/b027287a884fc2e173a65601ec242676 1) This is a very simplified example, but what I'm trying to do here is to call `foo` on each object in `Container.ss` contains when `foo` is called, and likewise for `bar`. To do this without having to repeat the foreach loop in every member function, I made the `call_for_each` template. However, I found no other way to pull this off (without using string mixins) than to also add the `call` template in the S struct. At first I thought it would be possible to write `s.func(args)` in `call_for_each`, but that will try to look up func as a member in the struct. Is there a more common / idiomatic way of doing this? In C++ this would be solved by using a member function pointer as a template argument, but as far as I understand D uses delegates (which are already bound to an instance) instead? 2) This is about the reduce templates. As I've commented, I can't use a template lambda with reduce, but I can use a lambda taking ints as arguments. Why is this? The error message I get when using the template lambda is: "template instance reduce!((a, b) => a + b) cannot use local '__lambda1' as parameter to non-global template reduce(alias fun)()"
