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c#generics
SigTerm
SigTerm

Reputation: 26409

C# generics: default non-null value for member

In this generic "class":

public class Param<ValueType>{
    public ValueType value;
}

When ValueType is string I want value to be non-null for all newly created instances of class without explicitly passing default value through constructor. In my scenario ValueType can only be int, float, bool, string or struct (that doesn't need to be enforced).

How can I do that?

When I try to do this:

public class Param<ValueType> where ValueType: new(){
    public ValueType value = new ValueType();
}

class stops accepting strings.

When I remove new() constraint, I can no longer use new ValueType() (obviously) and value is null for all new instances of Param<string>.

What can I do about it?

The reason why I want this to happen is because I have .Equals() defined which does value.Equals(other.value), which causes exception to be thrown when value is null.

Upvotes: 2

Views: 1423

Answers (1)

xanatos
xanatos

Reputation: 111810

You could:

public class Param<ValueType>
{
    public ValueType value = typeof(ValueType) == typeof(string) ? (ValueType)(object)string.Empty : default(ValueType);
}

note that default(int) == 0 and so on.

Ah and for the comparison, you should:

bool areEqual = EqualityComparer<ValueType>.Equals(value, other.Value);

It correctly works for null values.

Note even that with generics, this:

if (value == null)
{

}

is perfectly valid code. Clearly it will be true only if ValueType can be null and is null (so for ValueType == int it won't ever happen)

Upvotes: 3

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