gmpxx implicit conversion between types
marc.glisse at inria.fr
Sat Mar 5 21:20:38 CET 2011
currently, gmpxx has implicit conversions between all types. For instance,
if I have:
this last call is ambiguous as q+q can just as well be converted to a
mpz_class as a mpq_class. Without the second line, q+q would silently be
converted to an integer, which I think is scary.
One thing that would be possible is making it so that this conversion is
only possible if explicitly asked for, like mpz_class(q+q), but doesn't
happen implicitly in f(q+q). It wouldn't change the fact that any integral
expression can implicitly be converted to a rational, which is ok.
More generally, we would need to decide which conversions should be
implicit and which explicit between mpz_class, mpq_class and mpf_class (I
never use that last one which is why I am not using it as an example).
In case you are interested, I hit this while trying to make a generic
fraction creator that takes two numbers n and d and returns a fraction
n/d. If n or d is already a fraction, I just do a division. If n and d are
both convertible to a numerator (resp. denominator) type, then I compose
them. This convertibility test fails with gmpxx.
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