The errors raised by the numeric-numeric conversion function in std.conv are inaccurate in two ways:
1. Both underflowing and overflowing conversions raise a ConversionOverflowError, with the following respective messages presented to the user:
std.conv.ConvOverflowError: Error: overflow Conversion underflow
std.conv.ConvOverflowError: Error: overflow Conversion overflow
2. Converting a floating-point NaN to an integer type gives an underflow error.
Suggestions for simple fixes:
1. At the very least, the "overflow" string which is added to both over- and underflow errors should be removed from ConvOverflowError.
2. Put the following at the top of the "to" function definition:
static if (isFloatingPoint!S && !isFloatingPoint!T)
if (isNaN(value)) ConvOverflowError.raise("Cannot convert "
~S.stringof~".nan to "~T.stringof);
(Of course, it is arguable whether the slightly more accurate error message is worth the performance penalty of the additional check...)