On Tuesday, 22 February 2022 at 13:53:34 UTC, steve wrote:
On Monday, 21 February 2022 at 23:07:44 UTC, Ali Çehreli wrote:
On 2/21/22 12:44, steve wrote:
...
thanks for your help. I'm unfortunately still a bit confused.
Maybe I wasn't clear or maybe I'm just missing something here.
What I was trying to return is function that can then be
applied to e.g. an array. As I understand the mapped function
you wrote expects a range and a function argument something
that would let me do
```d
float my_function(float x){ return 2*x;}
auto my_function_mapped = mapped(my_function);
assert(my_function_mapped([1.,2.,3.]) == [2.,4.,6.]);
```
`map` does not eagerly allocate or process data. `map` is
actually a lazy function, meaning it doesn't actually run until
you look at the elements.
If you want a *concrete* range, you can use `array` from
`std.array` as follows:
```d
float[] get_map(alias f)(float[] input){
import std.algorithm : map;
import std.array : array;
return input.map!(f).array;
}
```
`array` iterates all elements in the range and allocates a new
array to hold the data.
I know in other languages, people are used to just using arrays
for all high-level composition, but D tries not to incur the
allocation/copy penalty if it can help it. So it's worth
questioning if you actually need an array, or if you can just use
the map result directly.
-Steve
