In the style guide it says that functions that modify their arguments should be marked with a !. However in the example given the function double! returns the modified argument a. Why return it if it has already been modified? Is it necessary?
Should a ! function return anything?
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1 Answers
It doesn't cost anything and enables you do things like:
b = double!(a)*x
or
double!(double!(a))
in a single line if you needed to.
For that reason (i.e. convenience), it has become convention.
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