Is it better to cast double as decimal or construct "new" decimal from double?

Question

When going from a double to a decimal, presuming my double can be represented as a decimal...

Is it more appropriate to cast a double as a decimal:
(Explicit Numeric Conversions Table) (Note that this entry erroneously contradicts the former!)

double foo = bar; decimal foobar = (decimal)foo; 

Or is it more appropriate to call the decimal constructor:
(Decimal Constructor)

double foo = bar; decimal foobar = new decimal(foo); 

I tend to use the decimal constructor, but I wonder reasons to use one versus the other.

From what I can tell the only difference is that an explicit cast of a double below Decimal.MinValue returns a zero, while using the constructor throws an OverflowException

EDIT: @Joren in the comments below notes that the cast throws an OverflowException for small values as well... so apparently the MSDN documentation is incorrect.

Related Questions:
- C# cast a double variable to decimal
- Automatically cast from double to decimal safely: Is the following safe?

Answer 1

There's really no difference. Using ILSpy:

// decimal public static explicit operator decimal(double value) {     return new decimal(value); } 

Based on examining the IL with LINQPad, the operator overload is called the same way in checked and unchecked contexts in C#.

In Visual Basic, CDec([double]) and CType([double],Decimal) calls the constructor directly, so there's no difference in that regard, but the cast is more able to participate in compile-time constant-folding than the constructor.

Answer 2

I would rather go for the constructor then! At least you get informed that your value is out of limits instead of setting it to 0 silently! The documentation says:

The explicit numeric conversion may cause loss of precision or result in throwing exceptions.

If one does not really care about precision than casting can be used. In the other hand, if you are playing with money for example, the last thing you would do is rounding off doubles! You don't want your application to turn valuable decimal fractions to 0 where you do not expect it to do so.