Proposal: Save space by removing delegates from TryPick and Map autogenerated implementations

[zspitz]

The autogenerated code for the TryPickX method currently looks like this:

public OneOf<T0, T1, TResult, T3> MapT2<TResult>(Func<T2, TResult> mapFunc)
{
    if(mapFunc == null)
    {
        throw new ArgumentNullException(nameof(mapFunc));
    }
    return Match<OneOf<T0, T1, TResult, T3>>(
        input0 => input0,
        input1 => input1,
        input2 => mapFunc(input2),
        input3 => input3
    );
}

Each delegate requires the compiler to generate its own class. Similarly, for Map:

public OneOf<T0, T1, TResult, T3> MapT2<TResult>(Func<T2, TResult> mapFunc)
{
    if(mapFunc == null)
    {
        throw new ArgumentNullException(nameof(mapFunc));
    }
    return Match<OneOf<T0, T1, TResult, T3>>(
        input0 => input0,
        input1 => input1,
        input2 => mapFunc(input2),
        input3 => input3
    );
}

Using autogenerated implementations that don't have delegates, e.g. for TryPick:

public bool TryPickT1(out T1 value, out OneOf<T0, T2, T3, T4> remainder)
{
    value = IsT1 ? AsT1 : default;
    switch (_index)
    {
        case 0: remainder = OneOf<T0, T2, T3, T4>.FromT0(AsT0); break;
        case 1: remainder = default; break;
        case 2: remainder = OneOf<T0, T2, T3, T4>.FromT1(AsT2); break;
        case 3: remainder = OneOf<T0, T2, T3, T4>.FromT2(AsT3); break;
        case 4: remainder = OneOf<T0, T2, T3, T4>.FromT3(AsT4); break;
        default: throw new InvalidOperationException();
    }
    return IsT1;
}

and for Map

public OneOf<T0, TResult, T2, T3, T4> MapT1<TResult>(Func<T1, TResult> mapFunc)
{
    if(mapFunc == null)
    {
        throw new ArgumentNullException(nameof(mapFunc));
    }
    switch (_index)
    {
        case 0: return OneOf<T0, TResult, T2, T3, T4>.FromT0(AsT0);
        case 1: return OneOf<T0, TResult, T2, T3, T4>.FromT1(mapFunc(AsT1));
        case 2: return OneOf<T0, TResult, T2, T3, T4>.FromT2(AsT2);
        case 3: return OneOf<T0, TResult, T2, T3, T4>.FromT3(AsT3);
        case 4: return OneOf<T0, TResult, T2, T3, T4>.FromT4(AsT4);
        default: throw new InvalidOperationException();
    }
}

reduces the file size, as follows:

File	Current	Reduced
OneOf.dll	233K	106K
OneOf.Extended.dll	9.9M	1.9M

I've never had much need to consider this before, but I'm wondering if there are other ways to reduce the size of the IL? Maybe use later language features such as switch expressions? Or perhaps replace internal calls to FromX with a generic FromIndex method with a generic parameter?

How much of a reduction would be needed to move OneOf.Extended back into the original dll?

[mcintyre321]

This is really good stuff, a big win! Will welcome PR with open arms. It would be an interesting exercise to see what the addembly sizes are if c# 9 static lambdas were used with the original code. Would they be optimized away, or still take up lots of space...

…

On Mon, 28 Dec 2020, 2:06 pm Zev Spitz, ***@***.***> wrote: The autogenerated code for the TryPickX method currently looks like this: public OneOf<T0, T1, TResult, T3> MapT2<TResult>(Func<T2, TResult> mapFunc) { if(mapFunc == null) { throw new ArgumentNullException(nameof(mapFunc)); } return Match<OneOf<T0, T1, TResult, T3>>( input0 => input0, input1 => input1, input2 => mapFunc(input2), input3 => input3 ); } Each delegate requires the compiler to generate its own class. Similarly, for Map: public OneOf<T0, T1, TResult, T3> MapT2<TResult>(Func<T2, TResult> mapFunc) { if(mapFunc == null) { throw new ArgumentNullException(nameof(mapFunc)); } return Match<OneOf<T0, T1, TResult, T3>>( input0 => input0, input1 => input1, input2 => mapFunc(input2), input3 => input3 ); } Using autogenerated implementations that don't have delegates, e.g. for TryPick: public bool TryPickT1(out T1 value, out OneOf<T0, T2, T3, T4> remainder) { value = IsT1 ? AsT1 : default; switch (_index) { case 0: remainder = OneOf<T0, T2, T3, T4>.FromT0(AsT0); break; case 1: remainder = default; break; case 2: remainder = OneOf<T0, T2, T3, T4>.FromT1(AsT2); break; case 3: remainder = OneOf<T0, T2, T3, T4>.FromT2(AsT3); break; case 4: remainder = OneOf<T0, T2, T3, T4>.FromT3(AsT4); break; default: throw new InvalidOperationException(); } return IsT1; } and for Map public OneOf<T0, TResult, T2, T3, T4> MapT1<TResult>(Func<T1, TResult> mapFunc) { if(mapFunc == null) { throw new ArgumentNullException(nameof(mapFunc)); } switch (_index) { case 0: return OneOf<T0, TResult, T2, T3, T4>.FromT0(AsT0); case 1: return OneOf<T0, TResult, T2, T3, T4>.FromT1(mapFunc(AsT1)); case 2: return OneOf<T0, TResult, T2, T3, T4>.FromT2(AsT2); case 3: return OneOf<T0, TResult, T2, T3, T4>.FromT3(AsT3); case 4: return OneOf<T0, TResult, T2, T3, T4>.FromT4(AsT4); default: throw new InvalidOperationException(); } } reduces the file size, as follows: File Current Reduced OneOf.dll 233K 106K OneOf.Extended.dll 9.9M 1.9M I've never had much need to consider this before, but I'm wondering if there are other ways to reduce the size of the IL? Maybe use later language features such as switch expressions? Or perhaps replace internal calls to FromX with a generic FromIndex method with a generic parameter? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#72>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AACDJ6T2CL7UP35HLCNAR4LSXCGF3ANCNFSM4VMCFV7A> .

[zspitz]

Would you consider using a higher C# language version? Most of the new syntax is supported even on earlier framework versions (https://medium.com/@SergioPedri/enabling-and-using-c-9-features-on-older-and-unsupported-runtimes-ce384d8debb). Switch expressions in particular could be very useful.

If nothing else, it would make the auto-generated code easier to maintain, by outputting less.

[zspitz]

Using static doesn't seem to make much of a difference. Looking at the output dll with ILSpy, the compiler-generated classes are all still there.

Another observation: Release is slightly smaller than Debug:

File	Debug	Release
OneOf.dll	240K	230K
OneOf.Extended.dll	9.8M	9.7M

@mcintyre321 Can I set the language version to C# 9? Even though there are some parts of C# 9 that aren't supported on older framework versions? As I noted above, it'll make the autogenerated code easier to maintain.