How to provide this arg or functor for algorithm?

[FreeSlave via Digitalmars-d-learn]

On Sunday, 16 August 2015 at 12:30:54 UTC, cym13 wrote:
> On Sunday, 16 August 2015 at 11:53:42 UTC, FreeSlave wrote:
>> [...]
>
> Ok, so as my lambda proposition obviously doesn't work, here is 
> one way that does using a templated function. There may be a 
> way to make it shorter, I don't know.
>
>
>     import std.conv;
>     import std.stdio;
>
>     template fun(uint context) {
>         static uint withContext(uint value) {
>             return value * context;
>         }
>
>         auto fun(uint[] arr) @nogc {
>             return arr.map!withContext;
>         }
>     }
>
>     void main(string[] args) {
>         [1, 2, 3].to!(uint[])
>                  .fun!2
>                  .writeln;
>     }

It works only because 2 is known constant at compile time.