Re: Alternative to friend functions?
On Thursday, 20 February 2020 at 08:02:48 UTC, Bienlein wrote:
On Tuesday, 18 February 2020 at 12:43:22 UTC, Adnan wrote:
What is the alternative to C++'s friend functions in D?
module stable_matching;
alias FemaleID = int;
alias MaleID = int;
class Person {
string name;
int id;
}
class Male : Person {
this(string name = "Unnamed Male") {
static int nextID = 0;
this.id = nextID++;
this.name = name;
}
}
class Female : Person {
this(string name = "Unnamed Female") {
static int nextID = 0;
this.id = nextID++;
this.name = name;
}
}
class Husband(uint N) : Male {
FemaleID engagedTo = -1;
const FemaleID[N] preferences;
this(FemaleID[N] preferences) {
this.preferences = preferences;
}
}
class Wife(uint N) : Female {
FemaleID engagedTo = -1;
const MaleID[N] preferences;
this(MaleID[N] preferences) {
this.preferences = preferences;
}
}
void engage(N)(ref Wife!N, wife, ref Husband!N husband) {
// Here, I want to access both husband and wife's
engaged_to
}
class MatchPool(uint N) {
Husband!N[N] husbands;
Wife!N[N] wives;
}
I would make Husband and Wife subclasses of a common abstract
superclass Spouse that declares the engagedTo var. The Spouse
superclass would also be the place where to put the engage
method. What is different for males and females you can
redefine in the respective subclass.
But where in that inheritance hierarchy will you slot the Spouse
class in? You don't have multiple inheritance in D, so are you
thinking along these lines?:
class Person {..}
class Spouse : Person {..}
class Male : Spouse {..}
class Female : Spouse {..}
That implies every Male and Female 'is a' Spouse which, feels a
bit clunky to me.
Maybe a better design for your idea is to make Spouse an
interface; something along these lines:
class Person {..}
interface Spouse {void engage(..);}
class Male : Person, Spouse {..}
class Female : Person, Spouse {..}
Then, as you say, the respective engage(..) implementations are
done in the Male/Female subclass.
Maybe you can even declare a winArgument(..) method returning a
bool in the Spouse interface. For the Male class the
implementation will be real easy: just return false!
[Disclaimer]: Last paragraph not to be taken seriously!
Re: Alternative to friend functions?
On Tuesday, 18 February 2020 at 12:43:22 UTC, Adnan wrote:
What is the alternative to C++'s friend functions in D?
module stable_matching;
alias FemaleID = int;
alias MaleID = int;
class Person {
string name;
int id;
}
class Male : Person {
this(string name = "Unnamed Male") {
static int nextID = 0;
this.id = nextID++;
this.name = name;
}
}
class Female : Person {
this(string name = "Unnamed Female") {
static int nextID = 0;
this.id = nextID++;
this.name = name;
}
}
class Husband(uint N) : Male {
FemaleID engagedTo = -1;
const FemaleID[N] preferences;
this(FemaleID[N] preferences) {
this.preferences = preferences;
}
}
class Wife(uint N) : Female {
FemaleID engagedTo = -1;
const MaleID[N] preferences;
this(MaleID[N] preferences) {
this.preferences = preferences;
}
}
void engage(N)(ref Wife!N, wife, ref Husband!N husband) {
// Here, I want to access both husband and wife's engaged_to
}
class MatchPool(uint N) {
Husband!N[N] husbands;
Wife!N[N] wives;
}
I would make Husband and Wife subclasses of a common abstract
superclass Spouse that declares the engagedTo var. The Spouse
superclass would also be the place where to put the engage
method. What is different for males and females you can redefine
in the respective subclass.
Re: Alternative to friend functions?
On Tuesday, 18 February 2020 at 12:43:22 UTC, Adnan wrote:
class Wife(uint N) : Female {
FemaleID engagedTo = -1;
const MaleID[N] preferences;
this(MaleID[N] preferences) {
this.preferences = preferences;
}
}
void engage(N)(ref Wife!N, wife, ref Husband!N husband) {
// Here, I want to access both husband and wife's engaged_to
}
Petar's answer covers your question, so I won't elaborate on
that, but I'd like to point out that as Wife and Husband are
classes, you probably don't intend to take them by ref - classes
are always by ref in D, so you're effectively passing a reference
to a reference to a class in `engage`.
Basically:
class Foo {
int n;
}
void fun(Foo f) {
f.n = 3;
// Local copy of the reference - does not modify other
references.
f = null;
}
void gun(ref Foo f) {
f = null;
}
unittest {
Foo f = new Foo();
Foo g = f;
f.n = 17;
// f and g point to the same object:
assert(f.n == 17);
assert(g.n == 17);
fun(f);
// fun() changed the object that both f and g point to:
assert(f.n == 3);
assert(g.n == 3);
gun(f);
// gun() changed f to no longer point at the same object, but
left g untouched:
assert(f is null);
assert(g !is null);
assert(g.n == 3);
}
--
Simen
Re: Alternative to friend functions?
On Tuesday, 18 February 2020 at 12:43:22 UTC, Adnan wrote:
What is the alternative to C++'s friend functions in D?
module stable_matching;
alias FemaleID = int;
alias MaleID = int;
class Person {
string name;
int id;
}
class Male : Person {
this(string name = "Unnamed Male") {
static int nextID = 0;
this.id = nextID++;
this.name = name;
}
}
class Female : Person {
this(string name = "Unnamed Female") {
static int nextID = 0;
this.id = nextID++;
this.name = name;
}
}
class Husband(uint N) : Male {
FemaleID engagedTo = -1;
const FemaleID[N] preferences;
this(FemaleID[N] preferences) {
this.preferences = preferences;
}
}
class Wife(uint N) : Female {
FemaleID engagedTo = -1;
const MaleID[N] preferences;
this(MaleID[N] preferences) {
this.preferences = preferences;
}
}
void engage(N)(ref Wife!N, wife, ref Husband!N husband) {
// Here, I want to access both husband and wife's engaged_to
}
class MatchPool(uint N) {
Husband!N[N] husbands;
Wife!N[N] wives;
}
In D the unit of encapsulation is not class, but module, and so
`private` only restricts access from other modules. If `engage`
is declared in the same module as the classes, you should have no
problems accessing their private members.
If you want to put `engage` in a different module, than you can
use the `package` access modifier to allow all modules in a given
package to access `package` members.
Alternative to friend functions?
What is the alternative to C++'s friend functions in D?
module stable_matching;
alias FemaleID = int;
alias MaleID = int;
class Person {
string name;
int id;
}
class Male : Person {
this(string name = "Unnamed Male") {
static int nextID = 0;
this.id = nextID++;
this.name = name;
}
}
class Female : Person {
this(string name = "Unnamed Female") {
static int nextID = 0;
this.id = nextID++;
this.name = name;
}
}
class Husband(uint N) : Male {
FemaleID engagedTo = -1;
const FemaleID[N] preferences;
this(FemaleID[N] preferences) {
this.preferences = preferences;
}
}
class Wife(uint N) : Female {
FemaleID engagedTo = -1;
const MaleID[N] preferences;
this(MaleID[N] preferences) {
this.preferences = preferences;
}
}
void engage(N)(ref Wife!N, wife, ref Husband!N husband) {
// Here, I want to access both husband and wife's engaged_to
}
class MatchPool(uint N) {
Husband!N[N] husbands;
Wife!N[N] wives;
}
