bluss
commented
3 years ago Where and if to panic and where to check for the error involves some nonobvious choices. I'd prefer if "radix <= 18" is a precondition to calling "from_str_generic", i.e that this function doesn't have to care for possible 'i' as a digit and so on.
I'd also be fine to just have radix <= 16 as the requirement if that just seems easier to understand.
One alternative not explored here is to invent a new format for complex numbers - and use that for radix > 18. I don't have a great suggestion, but imagine if it was something like 1 + 0# where # is the imaginary unit - it needs to be some symbol that's not in ascii alphanumerics, unfortunately.
Playground link - showcase weird parses
As an example of a weird parse, "1i" is 38 as a real number in the type i32 with radix 20. But "1i + 1i" parses as the complex 38 + i in type Complex<i32> radix 20.
cuviper
bors[bot]
from_str_radix: Error if radix is > 18
Radix 19 and 20 introduce 'i' and 'j' as digits and this conflicts with how complex are parsed. Before this fix, it could parse
Num::from_str_radix("1ij + 1ij", 20)in a pretty surprising way.The
Numdocs already describe a rule for our situation - we might not support every radix in our implementation; we can return an error in this case instead.A new (internal) error kind is introduced for this.
It is necessary to preserve the previous panicking behaviour(?) for radix > 36 (this is what primitive types do - but other types are allowed to do differently, including never panicking).