Question

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Nullable types and the ternary operator. Why won’t this work?

This is my code which works

public decimal? Get()
{
    var res = ...
    return res.Count() > 0 ? res.First() : (decimal?) null;
}

and this one doesn’t work

public decimal? Get()
{
    var res = ...
    return res.Count() > 0 ? res.First() : null;
}

giving the compiler error:

Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between ‘decimal’ and ‘<null>‘

I wonder why? any ideas?

Answer 1

The error is pretty clear. Both the “?” en “:” parts of that conditional operator need to have the same type or must at least be implicitly converted to the same Type. And a lone null doesn’t have a good Type.

Maybe you could use .FirstOrDefault(). Depending on the type of your res that would give a null or 0m.