quantities can be assigned from cmath sqrt result, but not initialized

[edaskel@…]

The cmath functions are very helpful in letting me perform math on quantities, but I ran across an inconsistency. Code like:

    quantity<wavenumber, float> x, y;
    quantity<wavenumber, float> foo = sqrt(x*x + y*y);

fails to compile (with an "error: conversion from..."). The workaround is to use an assignment instead:

    quantity<wavenumber, float> foo;
    foo = sqrt(x*x + y*y);

It seems odd to have this restriction (and it's certainly undocumented) so I suspect it is a bug.

[edaskel@…]

minimal test case