Make computed property be calculated once in immutable record types-CodePudding

I was making an immutable record type with a computed property like this:

public record Example
{
    public int A { get; init; }
    public int B { get; init; }
    public int C => A * B;
}

Knowing that record field setters are init only, the value of example.C should never change for the lifespan of an example object.

In the example above, the computation behind the C property is very trivial, but for types with compute-intensive properties, caching could affect the speed of a program. Is there a simple way to make the property be calculated only once? Should it not be a default for immutable record types?

Of course one can abandon the idea of computed properties and do the computation in the constructor:

public record Example
{
    public int A { get; init; }
    public int B { get; init; }
    public int C { get; private init; }
    
    public Example(int A, int B)
    {
        C = A * B;
    }
}

But is there a way to do it without a constructor?

CodePudding user response：

I often use this pattern to lazily initialize expensive values that may or may not ever be referenced.

public record Example
{
    private int? _C;
    
    public int A { get; init; }
    public int B { get; init; }
    public int C => _C ??= (A * B);
}