Earlier quoted context omitted.
On technical side, I think GP meant stuff like this https://docs.microsoft.com/en-us/dotnet/api/system.span-1.-c... And this: https://docs.microsoft.com/en-us/dotnet/csharp/language-refe...
I know about spans and stackalloc, I mean quite literally does the word affordance mean something technical here that I've not come across?
Affordance means that the interface of something indicates clearly how it's supposed to be used and for what purpose. This is broader term and it applies to physical stuff like door handles or knife grips too. It's intuitive enough which is probably why previous poster was confused about your question.