s2=+s1
Means merely nothing more than applying the unary operator+()
to the rvalue
provided with the operator=()
‘s parameter.
That boils down to the same statement as
s2 = (+s1);
There’s no combined operator like operator+=()
for that.
That would have no effect at all, unless these operator functions are overloaded for specific (non primitive) types.
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solved What does =+ mean in c++ [duplicate]