Value Type Representation Between the Original and Revised C++

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re: Value Type Representation Between the Original and Revised C++

Wesner Moise — Thu, 26 Feb 2004 23:30:00 GMT

Feel free to delete my prior comments, if I had read more carefully your post, I would have not been confused.

re: Value Type Representation Between the Original and Revised C++

Wesner Moise — Thu, 26 Feb 2004 23:17:00 GMT

I guess the clarification I need from this post was that ToString() must be overridden, for boxing to be avoid.

re: Value Type Representation Between the Original and Revised C++

Wesner Moise — Thu, 26 Feb 2004 23:10:00 GMT

Of course, Complex is boxed in your example, because it is invoking System.ValueType::ToString. System.ValueType is a reference type!!

If you provide an overridden implementation of Complex.ToString. It will not be boxed.

The IL I get is the following:
L_0016: ldc.r8 1
L_001f: ldc.r8 2
L_0028: call Complex..ctor
L_002d: ldloca.s V_4
L_002f: call Complex.ToString
L_0034: stloc.3

Similarly, for primitive types, no boxing occurs with overridden calls to GetHashCode or ToString().

int i=2;
int k=3;
int j = i.GetHashCode();
string str = k.ToString();

L_0000: ldc.i4.2
L_0001: stloc.0
L_0002: ldc.i4.3
L_0003: stloc.1
L_0004: ldloca.s V_0
L_0006: call int.GetHashCode
L_000b: stloc.2
L_000c: ldloca.s V_1
L_000e: call int.ToString
L_0013: stloc.3

re: Value Type Representation Between the Original and Revised C++

Yves Dolce — Thu, 26 Feb 2004 23:07:00 GMT

Add

public override String ToString() { return String.Format( "{0} + {1} i", r.ToString(), i.ToString() ) ; }

to the struct and the boxing is gone:

IL_000d: ldloca.s c
IL_000f: ldc.r8 1.
IL_0018: ldc.r8 2.
IL_0021: call instance void NeedToBox.Complex::.ctor(float64, float64)
IL_0026: ldloca.s c
IL_0028: call instance string NeedToBox.Complex::ToString()

re: Value Type Representation Between the Original and Revised C++

Yves Dolce — Thu, 26 Feb 2004 22:51:00 GMT

I just tried with C#:
struct Complex
{
public Complex( double r, double i )
{
this.r = r ;
this.i = i ;
}
private double r, i ;
}

...

Complex c = new Complex( 1, 2 ) ;
c.ToString() ;

And the IL shows c IS boxed:

IL_000d: ldloca.s c
IL_000f: ldc.r8 1.
IL_0018: ldc.r8 2.
IL_0021: call instance void NeedToBox.Complex::.ctor(float64, float64)
IL_0026: ldloc.0
IL_0027: box NeedToBox.Complex
IL_002c: callvirt instance string [mscorlib]System.ValueType::ToString()

re: Value Type Representation Between the Original and Revised C++

Yves Dolce — Thu, 26 Feb 2004 22:38:00 GMT

Wesner,

Try calling ToString() on an instance of:

_value class Complex
{
public:
Complex( double r, double i ) : m_r(r), m_i(i) {}

public:
//virtual String * ToString() { return String::Format( S"{0} + {1} i", m_r.ToString(), m_i.ToString() ) ; }

private:
double m_r,
m_i ;
} ;

I will fail with:
error C3610: 'Complex': value type must be 'boxed' before method 'ToString' can be called

Uncomment the overriden ToString method or use the __box operator and it works.