For example:
int? qID= null;
answer.QuestionID = int.TryParse(lblID.Text, out qID.Value) ? qID : null; //Error: Property or Indexer may not be passed as an out ot ref parameter.
From microsoft documentation it says that:
"A variable passed as an out argument need not be initialized. However, the out parameter must be assigned a value before the method returns."
and then:
"A property is not a variable and cannot be passed as an out parameter.
So what was the reasoning in the underlying .net platform design to prohibit from setting a property of an object via the out? The value of out does not have to be a reference object either - totally legit to use a value type. So why not?
This is valid in VB, but not in C#... VB effectively creates a temporary local variable for you, calls the method passing in the local variable as the argument, and then sets the property with the value of the local variable. C# doesn't usually hide that sort of thing for you.
The method itself needs a variable as the out
parameter. It's got to have a storage location it can just write values to. Not a property, not anything it needs to invoke: just a storage location. A property doesn't satisfy that requirement. So there's nothing that can be done by the compiler in the method to allow this.
So either the compiler has to fake it with a temporary variable, as per VB, or disallow it, as per C#. Personally I prefer the C# approach - otherwise it looks as if each time the method assigned a value to the out parameter, the property would be set - which certainly isn't the case.
A property is just a pair of functions named get_Something
and set_Something
.
An out
parameter takes a reference to a field or a variable; it wouldn't make any sense to pass a pair of functions.
VB.Net can pass properties as ByRef
parameters; the compiler generates a temporary variable and re-assigns the proeprty to the variable after calling the method.
However, even VB.Net cannot handle your case, because the Nullable<T>.Value
property is read-only.
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