ryanhaining
`product` with repeats as an argument
Hi, I came here from doing Project Euler in C++.
I was googling for a library for doing product() and found this one, but it only allows a template argument.
My use-case is to have seq be the digits {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, and repeats be the number of them. This is required for some problems.
Having repeats would be great!
Sorry for the delayed response. You're not the first person to ask for something similar (see #41). The issue is that product is able to handle different types, and so must compute a lot at compile time. The flexibility you'd need would require a totally different product implementation that did work at runtime unless you know the repeat value that you need at compile time. Is that the case? So that something like product_repeat<3>(digits) could work for you?
Oh I basically need the same type but repeated different times, but the repeat value is not known at compile time.
A couple days ago I just did this manually by representing each possibility as a number, and extracting the digits. My set of digits were {1, 3, 7, 9}, and 1 encoded as 0, 3 encoded as 1, 7 encoded as 2, 9 encoded as 3, 11 encoded as 4 and so on. But some product() like Python's itertools I think will be more flexible.
The number of repeats is in a loop, so product_repeat<3>(digits) wouldn't work too well. It would if the loop was templated in some way, but that's not very nice.
Is it hard to make this a real parameter or would it slow things down lots? I'm guessing it'll be slower than the encoding scheme I had above, but hopefully not too much.
It's probably easier than implementing the existing version of product, the problem is that it's not a tweak, it's a from scratch implementation.
If you knew the upper bound and lower bounds at compile time you could maybe use c++20 consteval to do it, but it's not gonna be very elegant
On Tue, Jul 28, 2020, 1:49 AM simonzack [email protected] wrote:
Oh I basically need the same type but repeated different times, but the repeat value is not known at compile time.
A couple days ago I just did this manually by representing the product of digits as numbers, and extracting the digits. But some product() like Python's itertools I think will be more flexible.
The number of repeats is in a loop, so product_repeat<3>(digits) wouldn't work too well. It would if the loop was templated in some way, but that's not very pretty I'm guessing.
Is it hard to make this a real parameter or would it slow things down lots?
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Well I know the lower bound but not the upper bound.
And yes consteval & template stuff is not very elegant and seems like it's hard-coded. I barely know how to code template meta-programming stuff anyway.
I think the ideal form is something like Python and making it an argument. I think that's perfect if there's not a massive decrease in performance compared to just using a loop, encoding the indexes as numbers, and decoding it. That works but is rather tedious to code.
I'm not disagreeing about the ideal, it's just a totally different implementation than the existing product
On Wed, Jul 29, 2020, 2:17 AM simonzack [email protected] wrote:
Well I know the lower bound but not the upper bound.
And yes consteval & template stuff is not very elegant and seems like it's hard-coded. I barely know how to code template meta-programming stuff anyway.
I think the ideal form is something like Python and making it an argument. I think that's perfect if there's not a massive decrease in performance compared to just encoding the indexes in loops and decoding it that way. That works but is rather tedious to code.
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