Avoid boxing & unboxing in generic class

Question

Below is some quick code to illustrate my question. Any way to avoid this apparently unnecessary boxing/unboxing?

public class TestClass<T>
{
  public T TestMethod()
  {
    if (typeof(T) == typeof(bool))
    {
      return true; // doesn't work
      return (T)(object)true; // works, but any way to avoid this?
    }

    return default(T);
  }
}

Generics mean "same code works for multiple types". You want different code for different types, so your use-case is outside the focus of generics. — dtb, Nov 08 '12 at 21:19
If you're just going to check the type in the body of the method why make it generic in the first place? — Servy, Nov 08 '12 at 21:19
@dtb, @Servy: It's something similar to LINQ's `Cast(this IEnumerable source)`, but with a few custom cases such as "Y"/"N" needing manual conversion to true/false. If bool were my own type I could use an explicit operator. All the other types are handled generically. — Nelson Rothermel, Nov 08 '12 at 21:31
@TravisGockel: That may very well be true, but then it could only do it for the `TestClass` version of the generic. — Nelson Rothermel, Nov 08 '12 at 21:38
Casting `Func` is the way. See https://stackoverflow.com/questions/45507393 — cactuaroid, Jul 31 '21 at 14:52

score 4 · Accepted Answer · answered Nov 08 '12 at 21:18

4

This is the only way to handle what you are doing here (returning a non default value for a specific closed generic type).

answered Nov 08 '12 at 21:18

Oded

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This is what I figured since T isn't known at compile time, but I thought I would try. :) – Nelson Rothermel Nov 08 '12 at 21:50

score -1 · Answer 2 · answered Nov 08 '12 at 22:18

-1

Make it a static field.

public class TestClass<T>
{
  static T TrueIfBoolean = typeof(T) == typeof(bool) ? (T)(object)true : default(T)

  public T TestMethod()
  {
    return TrueIfBoolean;
  }
}

That way, the boxing/unboxing only happens once. It's also entirely possible that this kind of optimisation is done by the runtime anyway even in your initial code.

answered Nov 08 '12 at 22:18

Tar

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I don't think the compiler is allowed to optimize away a cast from a value type to `object`. On the other hand, if the cast only happens once, the time wasted is going to be a non-factor. – supercat Dec 18 '12 at 16:59

Avoid boxing & unboxing in generic class

2 Answers2