Nullable Convert ? : operand problem

[=?Utf-8?B?bWloa2VsdHQ=?=]

Just one question, why wouldn't the following lines compile:

decimal? decVar = 5;
int? intVar = decVar == null ? null :
Convert.ToInt32 (decVar.GetValu eOrDefault());

The compiler shows the following message: "There is no implicit conversion
between 'null' and 'int'."

A similar if-else construction works just fine.

Mihkel

[Marc Gravell]

Re: Nullable Convert ? : operand problem

As far as the ternary is concerned, it's two values are incompatible,
since "null" is interpreted as a null object, not the int? missing
value. You can re-educate it with a cast:

int? intVar = decVar == null ? (int?) null :
Convert.ToInt32 (decVar.GetValu eOrDefault());

Marc

[Jon Skeet [C# MVP]]

Re: Nullable Convert ? : operand problem

On Dec 5, 9:59 am, mihkeltt <mihke...@discu ssions.microsof t.com>
wrote:

Just one question, why wouldn't the following lines compile:
>
decimal? decVar = 5;
int? intVar = decVar == null ? null :
Convert.ToInt32 (decVar.GetValu eOrDefault());
>
The compiler shows the following message: "There is no implicit conversion
between 'null' and 'int'."
>
A similar if-else construction works just fine.

An int isn't convertible to null, and null isn't convertible to int -
you need to explain to the compiler which type to use that both values
*can* be converted to:

int? intVar = decVar==null ? (int?) null : Convert.ToInt32 (...);
or
int? intVar = decVar==null ? null : (int?)Convert.T oInt32(...);

Note that the code can be simplified somewhat:

However, for this code it's easier to just use:

int? intVar = (int?) decVar;

Jon

[Martin Hey]

Re: Nullable Convert ? : operand problem

you've to convert the null to a nullable int

decimal? decVar = 5;
int? intVar = decVar == null ? (int?)null :
Convert.ToInt32 (decVar.GetValu eOrDefault());


"mihkeltt" <mihkeltt@discu ssions.microsof t.comschrieb im Newsbeitrag
news:D948A17C-74A3-40BD-92D8-D976E41C0A36@mi crosoft.com...

Just one question, why wouldn't the following lines compile:
>
decimal? decVar = 5;
int? intVar = decVar == null ? null :
Convert.ToInt32 (decVar.GetValu eOrDefault());
>
The compiler shows the following message: "There is no implicit conversion
between 'null' and 'int'."
>
A similar if-else construction works just fine.
>
Mihkel

[=?Utf-8?B?bWloa2VsdHQ=?=]

Re: Nullable Convert ? : operand problem

then how is this statement different from the first one i've presented:

int? intVar = null;

this would work just fine.

"Marc Gravell" wrote:

As far as the ternary is concerned, it's two values are incompatible,
since "null" is interpreted as a null object, not the int? missing
value. You can re-educate it with a cast:
>
int? intVar = decVar == null ? (int?) null :
Convert.ToInt32 (decVar.GetValu eOrDefault());
>
Marc
>

[Jon Skeet [C# MVP]]

Re: Nullable Convert ? : operand problem

On Dec 5, 12:10 pm, mihkeltt <mihke...@discu ssions.microsof t.com>
wrote:

then how is this statement different from the first one i've presented:
>
int? intVar = null;
>
this would work just fine.

That's converting from null to int?, which is fine.

The conditional operator has to decide what the type of the overall
expression is. It does this by taking the two result types, and seeing
if it can convert from either one to the other. In this case, it
can't.

Jon

[=?Utf-8?B?bWloa2VsdHQ=?=]

Re: Nullable Convert ? : operand problem

thanks for the informative and quick reply, Jon.

Mihkel

"Jon Skeet [C# MVP]" wrote:

On Dec 5, 12:10 pm, mihkeltt <mihke...@discu ssions.microsof t.com>
wrote:

then how is this statement different from the first one i've presented:

int? intVar = null;

this would work just fine.

>
That's converting from null to int?, which is fine.
>
The conditional operator has to decide what the type of the overall
expression is. It does this by taking the two result types, and seeing
if it can convert from either one to the other. In this case, it
can't.
>
Jon
>

[Ben Voigt [C++ MVP]]

Re: Nullable Convert ? : operand problem


"Marc Gravell" <marc.gravell@g mail.comwrote in message
news:1fdf4779-5ae8-40b1-93b1-9f373e956803@e2 5g2000prg.googl egroups.com...

As far as the ternary is concerned, it's two values are incompatible,
since "null" is interpreted as a null object, not the int? missing
value. You can re-educate it with a cast:
>
int? intVar = decVar == null ? (int?) null :
Convert.ToInt32 (decVar.GetValu eOrDefault());

Furthermore (and to eliminate precedence confusion), don't compare Nullable
values to null.

Instead, use the HasValue property:

int? intVar = decVar.HasValue ? Convert.ToInt32 (decVar.GetValu eOrDefault()):
(int?) null;

>
Marc