CODEWITHSUNDEEP
c#.netc#-7.0
rory.ap
rory.ap

Reputation: 35270

Assign a value to an explicitly-implemented readonly interface property in a constructor

Same question as this one, but for C# 7.0 instead of 6.0:

Is there a way to assign a value to an explicitly-implemented read-only (getter only) interface property in a constructor? Or is it still the same answer, i.e. use the backing-field work-around?

For example:

interface IPerson
{
    string Name { get; }
}

class MyPerson : IPerson
{
    string IPerson.Name { get; }

    internal MyPerson(string withName)
    {
        // doesn't work; Property or indexer 'IPerson.Name' 
        // cannot be assigned to --it is read only
        ((IPerson)this).Name = withName; 
    }
}

Work-around:

class MyPerson : IPerson
{
    string _name;
    string IPerson.Name { get { return _name; } }

    internal MyPerson(string withName)
    {
        _name = withName; 
    }
}

Upvotes: 5

Views: 1458

Answers (2)

David Arno
David Arno

Reputation: 43254

As of C# 7, the best you can do is to take advantage of expression-bodied properties and constructors to slightly simplify your code:

class MyPerson : IPerson
{
    string _name;
    string IPerson.Name => _name;

    internal MyPerson(string withName) => _name = withName;
}

This doesn't directly address your question though: having a means of setting an interface-explicit property from the constructor. There is a proposal though that might address this in the future, but there are no guarantees.

Proposal: Property-Scoped Fields, which suggests allowing the contextual keyword field to be used within properties to refer to the backing field, without having to explicitly define the latter. It's possible that this might also provide syntax along the lines of:

string IPerson.Name { get; }
internal MyPerson(string withName) => IPerson.Name.field = withName;

However, the above link is to just a discussion topic on the C# language repo on GitHub. I hasn't (yet) been "championed" by the language team, which is the first step to it even being considered as a new feature. so the odds are this will never be added to the language (but things defy the odds sometimes, so never say never...)

Upvotes: 7

Robert Petz
Robert Petz

Reputation: 2764

No you still would require the same workaround in C# 7. If you were referring to expression bodied members being extended to the constructor, it does not have any effect that lifted this restriction.

Upvotes: 0

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