On 8/24/18 11:18 AM, Peter Alexander wrote:
Consider this code, which is used as an example only:
auto scaleAll(int[] xs, int m) {
return xs.map!(x => m * x);
}
As m is captured, the delegate for map will rightly allocate the closure
in the GC heap.
In C++, you would write the lambda to capture m by value, but this is
not a facility in D.
I can write scaleAll like this:
auto scaleAll(int[] xs, int m) @nogc {
return repeat(m).zip(xs).map!(mx => mx[0] * mx[1]);
}
So that repeat(m) stores m, but it is quite hacky to work like this.
I could write my own range that does this, but this is also not desirable.
Are there any established patterns, libraries, or language features that
can help avoid the GC allocation in a principled way here?
This is somewhat related to a suggestion I had last month:
https://forum.dlang.org/post/pjnue1$olt$1...@digitalmars.com
I also hate to have such a thing allocate. The only scalable solution I
can think of is to write your own range function which has the
appropriate state saved by value. But then you lose all the goodies from
Phobos.
Having a way to capture state and give that state to std.algorithm
ranges would be really cool.
-Steve
