C#•2mo ago

Any case where `TError` can't be boxed in example?

So I have the following:

public class ParseResult<TResult, TError>
{
    private readonly TResult? _result;
    private readonly TError? _error;

    private ParseResult(TResult? result, TError? error)
    {
        _result = result;
        _error = error;
    }

    public static ParseResult<TResult, TError> CreatedResult(TResult result)
        => new ParseResult<TResult, TError>(result, null);
}

public class ParseResult<TResult, TError>
{
    private readonly TResult? _result;
    private readonly TError? _error;

    private ParseResult(TResult? result, TError? error)
    {
        _result = result;
        _error = error;
    }

    public static ParseResult<TResult, TError> CreatedResult(TResult result)
        => new ParseResult<TResult, TError>(result, null);
}

But am getting an error on last line passing null in, I can see it resolves if i add a class constraint to the generic arg, or if i give default, but confused why it cant infer that TError? is always gonna be boxed, i.e. if i had int as TError surely it can work out Nullable<int> from TError?

5 Replies

pseudoOP•2mo ago

@pride century 젠젠 Sorry for ping but im actually still confused :TERROR: I get what you were saying about the .Value stuff

public class ParseResult<TResult, TError>
{
    private readonly TResult? _result;
    private readonly TError? _error;

    private ParseResult(TResult? result, TError? error)
    {
        _result = result;
        _error = error;
    }

    public bool IsError() => _error is not null;

    public TResult Result()
    {
        if (_result is null)
            throw new Exception("Given result type is an error");

        return (TResult) _result;
    }

    public static ParseResult<TResult, TError> CreatedResult(TResult result) 
        => new(result, default);

    public static ParseResult<TResult, TError> CreateError(TError error)
        => new(default, error);
}

public class ParseResult<TResult, TError>
{
    private readonly TResult? _result;
    private readonly TError? _error;

    private ParseResult(TResult? result, TError? error)
    {
        _result = result;
        _error = error;
    }

    public bool IsError() => _error is not null;

    public TResult Result()
    {
        if (_result is null)
            throw new Exception("Given result type is an error");

        return (TResult) _result;
    }

    public static ParseResult<TResult, TError> CreatedResult(TResult result) 
        => new(result, default);

    public static ParseResult<TResult, TError> CreateError(TError error)
        => new(default, error);
}

But how does this build fine with unconstrained type

    public TResult Result()
    {
        if (_result is null)
            throw new Exception("Given result type is an error");

        return (TResult) _result;
    }

    public TResult Result()
    {
        if (_result is null)
            throw new Exception("Given result type is an error");

        return (TResult) _result;
    }

I.e. this would crash surely for int?

alex•2mo ago

i dont know what you mean by boxing here

pseudoOP•2mo ago

sorry term for another lang Nullable<int> is boxed int altho is actually wrong if Nullable<T> is also a value-type, i just meant a nullable value type with it

alex•2mo ago

thats just a nullable value type and honestly dont put too much thought into it thats just how it works just make the fields unnullable and cope with it

pseudoOP•2mo ago

:TERROR: ty anyways

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Any case where `TError` can't be boxed in example?