Operator Precedence and Associativity has syntax rules for various operators and
a footnote says:
The operators
+,++and*are non-associative.
I am wondering about the semantics of various operator methods.
Are there guidelines about which operators should be commutative: for example, should
a + b == b + a
always hold? Where can I read about the properties that methods of various operators should have, in order to meet users’ expectations?