...requirements, are you looking for std.functionl.memoize?

auto fun(int a) {
    writeln("here");
    return...

...that string, rather than the string!

The memoize function is closer to what you want...

https://issues.dlang.org/show_bug.cgi?id=16079

--- Comment #4 from github-bugzilla@puremagic...

...cgi?id=18170
[Issue 18170] std.functional.memoize should be usable in @safe
https://issues...

https://issues.dlang.org/show_bug.cgi?id=18170

Seb <greensunny12@gmail.com> changed:

           What...

...18170

          Issue ID: 18170
           Summary: std.functional.memoize should be usable in @safe
           Product: D...

...S {

    int x;

    auto gen() @property {
      return memoize!doGen(this, x);
    }

  }

  void main() {
    S s...

something like this:

The error I got is:

I can't make doGen static because...

...joiner);
    writeln("-------------------------------");
    writeln((iota(1, 5).map!(memoize!parse)).joiner);
    writeln("-------------------------------");
    writeln((iota(1, 5...

...thing in an array than to use memoize. e.g.

auto arr = iota(1, 5...