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digitalmars.D - inconstant foo

reply Kevin Bealer <Kevin_member pathlink.com> writes:
I was thinking about "const" and I realized: D already has a form of const.
"The absence of a write method means that the property is read-only."

class const_foo {
char[] msg; /+ mutable member +/
int key() { return m_key; }

private:
int m_key;
};

/+ non-const foo +/
class foo : const_foo {
int key(int k) { m_key = k };
};

Now, functions that take a const_foo will not have access to key.  For those who
are about to say "this violates IS-a": Just imagine the adjective had the
opposite meaning; instead of "const foo" and "foo", think "readable foo" and
"readable writeable foo".

Kevin
May 11 2004
next sibling parent James McComb <alan jamesmccomb.id.au> writes:
Kevin Bealer wrote:

 Now, functions that take a const_foo will not have access to key.  For those
who
 are about to say "this violates IS-a": Just imagine the adjective had the
 opposite meaning; instead of "const foo" and "foo", think "readable foo" and
 "readable writeable foo".

I think you mean "writeable readable foo". :) I "writeable readable foo" IS A "readable foo". James McComb
May 11 2004
prev sibling parent J Anderson <REMOVEanderson badmama.com.au> writes:
Kevin Bealer wrote:

I was thinking about "const" and I realized: D already has a form of const.
"The absence of a write method means that the property is read-only."

class const_foo {
char[] msg; /+ mutable member +/
int key() { return m_key; }

private:
int m_key;
};

/+ non-const foo +/
class foo : const_foo {
int key(int k) { m_key = k };
};

Now, functions that take a const_foo will not have access to key.  For those who
are about to say "this violates IS-a": Just imagine the adjective had the
opposite meaning; instead of "const foo" and "foo", think "readable foo" and
"readable writeable foo".

Kevin



  

//common module 1 template ConstT(T) //This would be in another module { struct Const { private int val; static Const opCall(T val) { Const t; t.value = val; return t; } int value() { return val; } } } alias ConstT!(int).Const const; //module 2 void test(const value) { int x = value.value; //You just can't change the variable (well at least not without force). } void main() { int a; test(const(a)); //Ok there's a small bit of extra typing -> if D only had automatic boxing.... } -- -Anderson: http://badmama.com.au/~anderson/
May 11 2004