Why struct opEquals must be const?

Nick Sabalausky a at a.a
Sat Oct 16 23:57:02 PDT 2010

Is there a technical reason why the l- and r- values for opEquals must be 
const? If the restriction is purely for the intuitive notion that there's no 
heisenstructs, then I have an example I think might be worth consideration: 
lazy caching.

If comparison isn't always needed and requires a potentially expensive 
computation that isn't likely needed otherwise (for example, a wrapper for 
string that does case-insensitive comparisons, if it's used in a situation 
that does more assigning/slicing/etc than comparing), then it may make sense 
to wait until an opEquals is called, and then compute the information and 
cache it. But that requires mutating state and so can't be done in a struct 

'Course, if there is a technical reason for the restriction, then all this 
is moot.

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