Is it possible to avoid boxing when setting C# struct/class fields using reflection?

Question

Say I have a primitive value which I need to assign to some field using reflection. I know for sure that field is of the same primitive value type.

Is it possible somehow to set this value without boxing?

void SetFloat(object o, string name, float val)
{
  var type = o.GetType();
  var fld = type.GetField(name);
  fld.SetValue(o, val /*boxing happens here*/);
}

P.S. It's not about latency really, it's about possible GC pressure. I'm using Unity3D which uses veeeery old Mono version which in its turn uses a very non-optimal GC implementation. Every extra memory allocation counts :(

P.P.S I'm building my own C# based interpreter, avoiding reflection seems almost impossible.

Communication

As far as I can find, no, FieldInfo.SetValue() only has overloads accepting object newValue, so any value type you pass it will be boxed. – Bowstring

its not possible. it doesnt seem useful either. if you are worried about performance try not to use reflection. – Smarmy

The use of reflection at all is orders of magnitude more performance intensive than the effort spent boxing the value. Boxing a value is extremely fast, almost immeasurably fast in comparison to the difference between setting a field normally vs. using reflection. It's like asking if there's a way for you to avoid having to tie your shoes when you decide to walk from New York to Los Angeles instead of flying on a plane. – Illyes

Well, it's not about speed really, it's about possible GC pressure. I'm using Unity which uses veeeery old Mono version which in its turn uses a very non-optimal GC implementation. Every extra allocation counts :( – Communication

if its about possible GC pressure again dont use reflection. you are focusing to optimize 0.1% of your application while 99.9% remains unchanged ;) – Smarmy

@Communication Anything you'd try to do to avoid boxing would unquestionably require doing more than allocating one simple variable, and would consequently add GC pressure, not remove it. – Illyes

@M.kazemAkhgary I'm building a C# interpreter, it's quite hard to avoid reflection usage for this task. – Communication

@Illyes well, variables of primitive types and structs don't produce any GC overhead – Communication

@Communication Again, anything that you'd try to do to avoid the boxing would unquestionably require doing even more work than what is spent boxing a single value. It wouldn't reduce the GC pressure, it'd increase it. – Illyes

@Illyes sorry but I'm not convinced that doing more work is always going to increase GC pressure. I'm saying this since I've spent enormous amount of time optimizing my C# code in order to make it more GC friendly and in some cases it literally does much more than original version and yet it doesn't make any allocations. – Communication

Can you generate code dynamically? e.g. using Reflection.Emit or Expression.Compile? – Simard

@Simard I'm afraid no, there are certain reflection limitations under iOS. But thanks for the tips. – Communication

You might be able to obtain the setter method and cast it to a delegate type. Then invoke that delegate normally. – Simard

That might work indeed, however setters will be required for all fields... – Communication

This question is a discussion. The concept under discussion is clearly not possible as agreed by all, and this site is simply not for discussions about philosophy of whether it would be a good idea to do something theoretically. @servy and others I suggest click Close to help clear some of the incredible clutter in the Unity3d tag. OP, don't hesitate to ask another clear question if you wish. – Sexton

@JoeBlow The impossibility of this isn't clear to me. While I can't think of a way to accomplish it, the CLR has tricky low level corners which might allow this. I'd expect it to be possible, at least if you don't require verifiable code. – Simard

Does Unity3D support __makeref and SetValueDirect? – Digestible

It's upsetting to see this question not being answered and instead argued about "if its useful", since I too am looking into this exact same problem. Being impossible to do given the API is one thing, but the rest of the spam is not. @Communication did you ever resolve this? GC is incredibly sensitive and if you're doing this 1000x a second it hurts because the GC will invoke a clean up therefore stalling the frame. My work around has always been to manually write the code to set the values, but users want it to be automatic for them :( – Ranunculaceous

Answer 1

It is possible with field.SetValueDirect but the downside is you cannot use IL2CPP because it does not support this.

Ranunculaceous