What's the purpose of the 'in' keyword ?

[Russel Winder]

On Sun, 2018-05-27 at 13:10 +0000, Adam D. Ruppe via Digitalmars-d-learn
wrote:
> On Sunday, 27 May 2018 at 13:02:23 UTC, loloof64 wrote:
> > What's the purpose of this 'in' keyword ? I could not process a 
> > good Google request to get an answer.
> 
> It means you are taking the parameter in to look at, but not 
> modify or store.
> 
> Basically "const". (well, for now, literally "const" but that can 
> change with other details)

Is there an easy set of "rules" as to when to use 'const' and when to use
'in'?

In a situation where there are multiple ways of expressing the same concept
there needs to be idioms to guide people to do the right thing in a given
context.

-- 
Russel.
=========================================
Dr Russel Winder     t:+44 20 7585 2200
41 Buckmaster Road   m:+44 7770 465 077
London SW11 1EN, UK  w: www.russel.org.uk
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