write once type?

[sighoya]

On Friday, 30 April 2021 at 01:30:54 UTC, Steven Schveighoffer 
wrote:

> In my case, for value of a certain type in the loop, I was 
> storing a specific field from the first one I found, and then 
> verifying that all the other values of that type (not exactly 
> the same type, but similar) had the same value for that field, 
> otherwise it was an error.
>
> I could have done it in 2 loops, but it's wasteful.

I have problems to grok exactly what you're talking about, can 
you provide some neat and small example for this?