What is pure used for?

[zjh]

On Thursday, 25 November 2021 at 07:26:48 UTC, sclytrack wrote:
> My understanding is that pure is used for compiler optimization 
> in loops and expressions. It leaves out multiple calls if it 
> figures out it is not needed.
>

[one 
link](https://klickverbot.at/blog/2012/05/purity-in-d/#indirections-in-the-return-type) and [another](https://theartofmachinery.com/2016/03/28/dirtying_pure_functions_can_be_useful.html)