Set-only subscripts

[dabrahams (Dave Abrahams)]

[Cross-reference] related issues were covered in

Support for pure setters

IMO, a good setter behaves like it's setting a variable, because this is exactly what the assignment operator suggests. That is: you should be able to replace a sequence of writes to a setter by a single write with the last value and still have essentially the same end result; you should be able to reorder setter operations and still essentially get the same end result. "Essentially the same end result" means that it's okay if the logging output is different or if you wasted cycles in the pr…