Is there a way to override the default processing of the assignment operator
for one's own __value types ? I realize I can program my own Assign method,
and provide that for end-users of my class, but I would like to use
internally my own = operator for some of my value types, so I can say "x =
y;" rather than "x.Assign(y );".
The op_Assign operator seems impossibly broken since it takes __value copies
of the two objects. Perhaps there is some other way.
20  1420 
There is no way to overload the assign operator.
You may be able to get what you want by overloading a conversion operator to
convert from y to x; that would allow you to write "x = y";
--
Eric Gunnerson
Visit the C# product team at http://www.csharp.net
Eric's blog is at http://weblogs.asp.net/ericgu/
This posting is provided "AS IS" with no warranties, and confers no rights.
"Edward Diener" <ed******@tropi csoft.com> wrote in message
news:Ot******** ******@TK2MSFTN GP12.phx.gbl... Is there a way to override the default processing of the assignment
operator for one's own __value types ? I realize I can program my own Assign
method, and provide that for end-users of my class, but I would like to use
internally my own = operator for some of my value types, so I can say "x =
y;" rather than "x.Assign(y );".
The op_Assign operator seems impossibly broken since it takes __value
copies of the two objects. Perhaps there is some other way.
Eric Gunnerson [MS] wrote: There is no way to overload the assign operator.
That is unfortunately what I thought.
You may be able to get what you want by overloading a conversion
operator to convert from y to x; that would allow you to write "x =
y";
No I want to overload the default behavior when one says:
X x;
X y;
// Do something with x to change it.
y = x;
where X is one of my own __value classes.
I think it is a weakness of the CLR that one can't override this behavior to
supply one's own functionality instead of the default behavior for
user-defined __value types. I admit I am not sure what the default behavior
is, whether it is a byte-by-byte copy of data from x to y, or whether it is
a field-by-field copy of data from x to y, or whether it takes into account
property values and gets and sets the appropriate properties when moving the
data. I know that when X is a __value class with properties, I want the get_
and set_ method for each property to be called if I say y = x, but I suspect
that is not the case. That is the reason I was hoping to override the
default assignment somehow.
My workaround is to provide a 'void X::Assign(X)' in order to do the
assignment, so that instead of writing y = x, I would write instead
y.Assign(x), but this is much less natural than the normal assignment
operator and y = x.
Needless to say, in C++ one can overload the default assignment operator
with 'X & operator = ( X /* or const X & */);'. Maybe CLR should revisit
this inability and make changes in the future which allows overriding the
assignment operator for user-devined __value classes possible.
This posting is provided "AS IS" with no warranties, and confers no
rights. "Edward Diener" <ed******@tropi csoft.com> wrote in message
news:Ot******** ******@TK2MSFTN GP12.phx.gbl... Is there a way to override the default processing of the assignment
operator for one's own __value types ? I realize I can program my
own Assign method, and provide that for end-users of my class, but I
would like to use internally my own = operator for some of my value
types, so I can say "x = y;" rather than "x.Assign(y );".
The op_Assign operator seems impossibly broken since it takes
__value copies of the two objects. Perhaps there is some other way.
"Edward Diener" <ed******@tropi csoft.com> wrote in message
news:ei******** ******@tk2msftn gp13.phx.gbl... Eric Gunnerson [MS] wrote: There is no way to overload the assign operator.
That is unfortunately what I thought.
You may be able to get what you want by overloading a conversion
operator to convert from y to x; that would allow you to write "x =
y";
No I want to overload the default behavior when one says:
X x;
X y;
// Do something with x to change it.
y = x;
where X is one of my own __value classes.
I think it is a weakness of the CLR that one can't override this behavior
to supply one's own functionality instead of the default behavior for
user-defined __value types. I admit I am not sure what the default
behavior is, whether it is a byte-by-byte copy of data from x to y, or whether it
is a field-by-field copy of data from x to y, or whether it takes into
account property values and gets and sets the appropriate properties when moving
the data. I know that when X is a __value class with properties, I want the
get_ and set_ method for each property to be called if I say y = x, but I
suspect that is not the case. That is the reason I was hoping to override the
default assignment somehow.
My workaround is to provide a 'void X::Assign(X)' in order to do the
assignment, so that instead of writing y = x, I would write instead
y.Assign(x), but this is much less natural than the normal assignment
operator and y = x.
Needless to say, in C++ one can overload the default assignment operator
with 'X & operator = ( X /* or const X & */);'. Maybe CLR should revisit
this inability and make changes in the future which allows overriding the
assignment operator for user-devined __value classes possible.
Interesting...t his is one of those features(operat or overloading in general,
outside of mathematics of course) I think should be left to die a slow
death.
This posting is provided "AS IS" with no warranties, and confers no
rights. "Edward Diener" <ed******@tropi csoft.com> wrote in message
news:Ot******** ******@TK2MSFTN GP12.phx.gbl... Is there a way to override the default processing of the assignment
operator for one's own __value types ? I realize I can program my
own Assign method, and provide that for end-users of my class, but I
would like to use internally my own = operator for some of my value
types, so I can say "x = y;" rather than "x.Assign(y );".
The op_Assign operator seems impossibly broken since it takes
__value copies of the two objects. Perhaps there is some other way.
Edward Diener <ed******@tropi csoft.com> wrote: You may be able to get what you want by overloading a conversion
operator to convert from y to x; that would allow you to write "x =
y";
No I want to overload the default behavior when one says:
X x;
X y;
// Do something with x to change it.
y = x;
where X is one of my own __value classes.
I think it is a weakness of the CLR that one can't override this behavior to
supply one's own functionality instead of the default behavior for
user-defined __value types.
I have to say that I couldn't disagree more. One thing I *like* is
knowing what will happen on assignment (when only one type is involved,
and thus no implicit conversions) *without* having to look up the
details of the type.
If you want a way of creating a copy of a value, write a Copy method or
something similar (which I think is clearer than calling Assign on an
existing value) - but leave the rest of us with a system where we don't
need to wonder what every single line of code means, however simple!
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Daniel O'Connell wrote: "Edward Diener" <ed******@tropi csoft.com> wrote in message
news:ei******** ******@tk2msftn gp13.phx.gbl... Eric Gunnerson [MS] wrote: There is no way to overload the assign operator.
That is unfortunately what I thought.
You may be able to get what you want by overloading a conversion
operator to convert from y to x; that would allow you to write "x =
y";
No I want to overload the default behavior when one says:
X x;
X y;
// Do something with x to change it.
y = x;
where X is one of my own __value classes.
I think it is a weakness of the CLR that one can't override this
behavior to supply one's own functionality instead of the default
behavior for user-defined __value types. I admit I am not sure what
the default behavior is, whether it is a byte-by-byte copy of data
from x to y, or whether it is a field-by-field copy of data from x
to y, or whether it takes into account property values and gets and
sets the appropriate properties when moving the data. I know that
when X is a __value class with properties, I want the get_ and set_
method for each property to be called if I say y = x, but I suspect
that is not the case. That is the reason I was hoping to override
the default assignment somehow.
My workaround is to provide a 'void X::Assign(X)' in order to do the
assignment, so that instead of writing y = x, I would write instead
y.Assign(x), but this is much less natural than the normal assignment
operator and y = x.
Needless to say, in C++ one can overload the default assignment
operator with 'X & operator = ( X /* or const X & */);'. Maybe CLR
should revisit this inability and make changes in the future which
allows overriding the assignment operator for user-devined __value
classes possible.
Interesting...t his is one of those features(operat or overloading in
general, outside of mathematics of course) I think should be left to
die a slow death.
It is alive and well, fortunately, but I am not going to get into a polemic
about it. I know only too well the arguments on both sides ( C++ has had it
from its inception ) and I know how much I approve of it myself and that is
all I will say.
Clearly .NET supports it although it is not CLS compliant. I just wanted to
use it in my own code for clarity, while providing a CLS Assign member
function also for other .NET languages.
Rather than get into an argument about overriding the built-in = operator
for value types, I will present a situation where it may not do what I want
it to do. I have a value type, let us call it X as in the above example,
which has a property, and also an event which is triggered when the property
changes. So in my property set function, I trigger the event. If I assign
one X to another using the built-in = operator, does my property set
function get called or does the built-in = operator just copy the underlying
X data from one to the other ? If the latter, then my event never gets
triggered, and event handlers which need to know when the property changes
never get called when using = to assign one object of the value type to
another.
In the Assign member function of value type X, I assign the property from
one to another which assures that the event gets triggered. If I could
override the built-in assignment operator = , I would do the same. Obviously
I can use Assign instead, but I have to remember to use it rather than the
more natural = assignment.
This posting is provided "AS IS" with no warranties, and confers no
rights. "Edward Diener" <ed******@tropi csoft.com> wrote in message
news:Ot******** ******@TK2MSFTN GP12.phx.gbl...
Is there a way to override the default processing of the assignment
operator for one's own __value types ? I realize I can program my
own Assign method, and provide that for end-users of my class, but
I would like to use internally my own = operator for some of my
value types, so I can say "x = y;" rather than "x.Assign(y );".
The op_Assign operator seems impossibly broken since it takes
__value copies of the two objects. Perhaps there is some other way.
Jon Skeet [C# MVP] wrote: Edward Diener <ed******@tropi csoft.com> wrote: You may be able to get what you want by overloading a conversion
operator to convert from y to x; that would allow you to write "x =
y";
No I want to overload the default behavior when one says:
X x;
X y;
// Do something with x to change it.
y = x;
where X is one of my own __value classes.
I think it is a weakness of the CLR that one can't override this
behavior to supply one's own functionality instead of the default
behavior for user-defined __value types.
I have to say that I couldn't disagree more. One thing I *like* is
knowing what will happen on assignment (when only one type is
involved, and thus no implicit conversions) *without* having to look
up the details of the type.
If you want a way of creating a copy of a value, write a Copy method
or something similar (which I think is clearer than calling Assign on
an existing value) - but leave the rest of us with a system where we
don't need to wonder what every single line of code means, however
simple!
Do you feel the same thing about overriding other operators also, or is your
uncomfortablene ss just about overriding the assignment operator ? I am just
curious because it is fruitless to get into an argument about operator
overriding. Obviously most C++ programmers like me love it, since it has
been part of the language since its inception and we are very much aware of
its advantages and disadvantages, while many others who have never used it
dislike it, largely for the reason you have given.
Edward Diener <ed******@tropi csoft.com> wrote: I have to say that I couldn't disagree more. One thing I *like* is
knowing what will happen on assignment (when only one type is
involved, and thus no implicit conversions) *without* having to look
up the details of the type.
If you want a way of creating a copy of a value, write a Copy method
or something similar (which I think is clearer than calling Assign on
an existing value) - but leave the rest of us with a system where we
don't need to wonder what every single line of code means, however
simple!
Do you feel the same thing about overriding other operators also, or is your
uncomfortablene ss just about overriding the assignment operator ? I am just
curious because it is fruitless to get into an argument about operator
overriding. Obviously most C++ programmers like me love it, since it has
been part of the language since its inception and we are very much aware of
its advantages and disadvantages, while many others who have never used it
dislike it, largely for the reason you have given.
I feel wary about introducing any operator overloads. They should be:
a) Entirely natural
b) The kind of thing which is bound to be commonly used
c) Very explicitly documented
For instance, it's handy having == and + overridden for string, and
having DateTime's relationship with TimeSpan (e.g. DateTime-
DateTime=TimeSp an, DateTime+TimeSp an=DateTime etc). For a few standard
types, it's fine - because everyone knows about it. When it comes to
3rd party classes which other developers will be less familiar with, I
get much more dubious.
I'm pretty uncomfortable with explicit conversion operators, and very
uncomfortable with implicit conversion operators. It basically means
code is being called where it doesn't look like any is. (Properties are
relatively obvious by convention - otherwise I'd be doubtful about
them, too.)
I can see the advantages when you know what's going on - but I'm a
*very* big fan of making the code as readable as possible to someone
who may come to maintain my code without necessarily being as
intimately familiar with the rest of the codebase as I am.
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
"Edward Diener" <ed******@tropi csoft.com> wrote in message
news:ey******** *****@TK2MSFTNG P11.phx.gbl... Daniel O'Connell wrote: "Edward Diener" <ed******@tropi csoft.com> wrote in message
news:ei******** ******@tk2msftn gp13.phx.gbl... Eric Gunnerson [MS] wrote:
There is no way to overload the assign operator.
That is unfortunately what I thought.
You may be able to get what you want by overloading a conversion
operator to convert from y to x; that would allow you to write "x =
y";
No I want to overload the default behavior when one says:
X x;
X y;
// Do something with x to change it.
y = x;
where X is one of my own __value classes.
I think it is a weakness of the CLR that one can't override this
behavior to supply one's own functionality instead of the default
behavior for user-defined __value types. I admit I am not sure what
the default behavior is, whether it is a byte-by-byte copy of data
from x to y, or whether it is a field-by-field copy of data from x
to y, or whether it takes into account property values and gets and
sets the appropriate properties when moving the data. I know that
when X is a __value class with properties, I want the get_ and set_
method for each property to be called if I say y = x, but I suspect
that is not the case. That is the reason I was hoping to override
the default assignment somehow.
My workaround is to provide a 'void X::Assign(X)' in order to do the
assignment, so that instead of writing y = x, I would write instead
y.Assign(x), but this is much less natural than the normal assignment
operator and y = x.
Needless to say, in C++ one can overload the default assignment
operator with 'X & operator = ( X /* or const X & */);'. Maybe CLR
should revisit this inability and make changes in the future which
allows overriding the assignment operator for user-devined __value
classes possible.
Interesting...t his is one of those features(operat or overloading in
general, outside of mathematics of course) I think should be left to
die a slow death.
It is alive and well, fortunately, but I am not going to get into a
polemic about it. I know only too well the arguments on both sides ( C++ has had
it from its inception ) and I know how much I approve of it myself and that
is all I will say.
Clearly .NET supports it although it is not CLS compliant. I just wanted
to use it in my own code for clarity, while providing a CLS Assign member
function also for other .NET languages.
Rather than get into an argument about overriding the built-in = operator
for value types, I will present a situation where it may not do what I
want it to do. I have a value type, let us call it X as in the above example,
which has a property, and also an event which is triggered when the
property changes. So in my property set function, I trigger the event. If I assign
one X to another using the built-in = operator, does my property set
function get called or does the built-in = operator just copy the
underlying X data from one to the other ? If the latter, then my event never gets
triggered, and event handlers which need to know when the property changes
never get called when using = to assign one object of the value type to
another.
In the Assign member function of value type X, I assign the property from
one to another which assures that the event gets triggered. If I could
override the built-in assignment operator = , I would do the same.
Obviously I can use Assign instead, but I have to remember to use it rather than the
more natural = assignment.
The question here, in my mind anyway, is should that event be raised anyway?
Is x = y still x? or is it y with no handler? Thats part of what I am
worried about, an assignment that instead of performing proper value
semantic copying is used to copy only pieces of the value, breaking value
semantics. In my opinion when I set x to y, then any event handler
references recorded in x should be destroyed along with the other data in x,
and y should be put in its place. No event should be raised because the
property *didn't* change, the variable that originally contained the
property did, but that is an entirely different beast.
"Edward Diener" <ed******@tropi csoft.com> wrote in message
news:eV******** *****@TK2MSFTNG P11.phx.gbl... Jon Skeet [C# MVP] wrote: Edward Diener <ed******@tropi csoft.com> wrote: You may be able to get what you want by overloading a conversion
operator to convert from y to x; that would allow you to write "x =
y";
No I want to overload the default behavior when one says:
X x;
X y;
// Do something with x to change it.
y = x;
where X is one of my own __value classes.
I think it is a weakness of the CLR that one can't override this
behavior to supply one's own functionality instead of the default
behavior for user-defined __value types.
I have to say that I couldn't disagree more. One thing I *like* is
knowing what will happen on assignment (when only one type is
involved, and thus no implicit conversions) *without* having to look
up the details of the type.
If you want a way of creating a copy of a value, write a Copy method
or something similar (which I think is clearer than calling Assign on
an existing value) - but leave the rest of us with a system where we
don't need to wonder what every single line of code means, however
simple!
Do you feel the same thing about overriding other operators also, or is
your uncomfortablene ss just about overriding the assignment operator ? I am
just curious because it is fruitless to get into an argument about operator
overriding. Obviously most C++ programmers like me love it, since it has
been part of the language since its inception and we are very much aware
of its advantages and disadvantages, while many others who have never used it
dislike it, largely for the reason you have given.
Since I meant to clarify a bit in the other thread but forgot to before I
posted, I'll post this bit here.
I personally have nothing against responsible use of operator overloading,
like Jon I like being able to overload == when appropriate, and having
string +string and other such short cuts is handy, however some constructs
are fincky and unpleasent(and considering the .NET implementation of
operator overloading, some things are a little t0o fussy anyway). The
feature is powerful, but dangerous, and I frown more upon unfettered and
irresponsible use of the feature than the feature itself. I see far too
often, even in C#, where an operator overload is done simply because the
original programer would rather type + or because he doesn't want to
explicitly cast, that kind of behaviour is troubling.
And, while those experianced in C++ will be discriminating( although not
always to my tastes), its not the masters I worry about, they, unfortunate
as it may be, are the minority. It is the mediocre and the amateur
programmer that will usually cause real damage with operator overloading.
Now, that said, I do have a particular problem with overloading the
assignment operator, as I addressed in part in my other posts. I simply
don't like to be guessing what I'm actually doing in the simplist line of
code possible in the language I'm working in. I don't think I'd like to find
a ref type that is always actually a value assignement, nor do I want to
find value assignments that aren't really value assignments, but partial
copies into the existing valuetype. Its just to complicated and it is far
too easy to get caught in a surprise because of it. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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Is there a way to override the default processing of the assignment operator
for one's own __value types ? I realize I can program my own Assign method,
and provide that for end-users of my class, but I would like to use
internally my own = operator for some of my value types, so I can say "x =
y;" rather than "x.Assign(y);".
The op_Assign operator seems impossibly broken since it takes __value copies
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