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The value type

  • Artigo

Last time, I discussed the ref
type.  This time, I'm going to talk about the value type.  This is the
CLR type exposed in Managed Extensions by the __value keyword,
and available in Whidbey C++ using the context-sensitive
keyword value.

What is a value type?   I view value types as a convenient way
to lump data together.  This isn't to say it has no member functions - it might
well - but the concept is of a chunk of data.  Where you might use a ref type
to implement a linked list class, a value type might be the right choice for the nodes
in that linked list.

What makes a value type different from a ref type?   Value
types can go almost anywhere: on the stack, as members of a ref class, passed
to functions, returned from functions, and even on the gc
heap.  They are considerably more lightweight than ref types.  However,
unlike ref classes, they cannot be inherited from.

Okay, well that sounds simple.  There's one more wrench
in the works: there's a special subset of value types called simple value
types.  These are value types that don't contain any handles (^) as members. 
With this restriction comes a benefit: simple value types can be allocated on the
native heap.

Let's look at the code for a value class:

  value class Point{

private:

int x,y;

public:

Point(int a, int b):x(a), y(b){}

int GetX(){ return x; }

int GetY(){ return y; }

void set(int a, int b){ x=a;
y=b; }

};

This is a good example of a simple value type, because it contains no handle (^) members. 

Value types aren't too complicated, as you can plainly see.  In a future code
sample, we'll look at implementing a basic data structure using completely managed
code.

Comments

  • Anonymous
    June 07, 2008
    Last time, I discussed the ref type .  This time, I'm going to talk about the value type.  This is the CLR type exposed in Managed Extensions by the __value keyword, and available in Whidbey C++ using the context-sensitive keyword value
  • Anonymous
    June 15, 2009
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