* having an implicit narrowing conversion from double to bigint is a bad idea, it should be explicit (it isn't completely obvious from the doc if that is the case).
It's pretty hard to have some constructor conversions implicit and others explicit. Might be possible with enable_if though. Will investigate.
It's a good comment. You know, a third of the people want it one way, another third want it the other way and the others don't care. You know, my initial design of the floating-point type did not feature this kind of conversion. But my opinion differed from the established one of boost and I adapted to boost when writing for boost. In fact, I believe that Boost.Math already set the bar on this one because when using Boost.Math with an extended precision type (this is possible), all implicit conversions to/from the built-in types are supported. I believe it would be incorrect to treat interaction with built-in types behave one way in Boost.Math and a different way in a potential Boost.Multiprecision. This is my opinion. Others will have different opinions. Best regards, Chris.