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digitalmars.D - Automatic Casting

reply Trevor Parscal <Trevor_member pathlink.com> writes:
I am working on a class that will interact with other numeric types. I want to
not have to manually class things all the time, and also want to be able to use
the class directly instead of a subfunction of the class... Like this..

class FOO
{
..?
}

FOO foo = new FOO();
foo = 5; // See how I can just give a numeric value to it
float bar = 5;
foo += bar; // And interact with other types
// foo now equals 10

Is this possible? I guess I want to make an int-like class. How do you do this?

Thanks,
Trevor Parscal
Dec 30 2005
next sibling parent "Unknown W. Brackets" <unknown simplemachines.org> writes:
The += thing is doable, but not =.  This is called implicit casting, and 
can cause confusing errors when misused.

Nonetheless, such things are sometimes very desirable, so it can be a 
conflicted issue many people argue over.

-[Unknown]


 I am working on a class that will interact with other numeric types. I want to
 not have to manually class things all the time, and also want to be able to use
 the class directly instead of a subfunction of the class... Like this..
 
 class FOO
 {
 ..?
 }
 
 FOO foo = new FOO();
 foo = 5; // See how I can just give a numeric value to it
 float bar = 5;
 foo += bar; // And interact with other types
 // foo now equals 10
 
 Is this possible? I guess I want to make an int-like class. How do you do this?
 
 Thanks,
 Trevor Parscal

Dec 30 2005
prev sibling next sibling parent Manfred Nowak <svv1999 hotmail.com> writes:
Trevor Parscal wrote:

[...]
 FOO foo = new FOO();
 foo = 5; // See how I can just give a numeric value to it

We all know that Walter is against overloading the `= operator. Therefore this is semantically wrong. When seeing this I would implement it as an opCall: foo(5); Therebye reinterpreting the OpCall as an assignment. Then Foo foo, bar; // snip foo(bar); // is an assignment of values This is different to foo= bar; // is an assignment of pointers. You cannot have both, when you in fact write `foo( bar)' as `foo= bar' So it seems to be possible 1) to have one xor the other depending on whether the magical opCall `Foo opCall( Foo <id>)' is declared. If it is declared, then the form `foo( ... )' is semantically disallowed and all calls of every `opCall' must have the form `foo= ...'. If it is not declared vice versa. 2) to have both, if we 2a) allow an unnamed attribute to a class. An unnamed attribute is represented by no name ;-), i.e. foo. = bar; The unnamed attribute represents the call of an `opCall', i.e. foo. = bar; is equivalent to foo( bar); is equivalent to foo.opCall( bar); Because expressions like foo. . . = bar; seems to have no sense, this leads to the 3rd alternative: 2b) create a new operator `.=' according to the above, where every foo .= bar; is equivalent to foo( bar); is equivalent to foo.opCall( bar); -manfred
Dec 31 2005
prev sibling parent Hasan Aljudy <hasan.aljudy gmail.com> writes:
Trevor Parscal wrote:
 I am working on a class that will interact with other numeric types. I want to
 not have to manually class things all the time, and also want to be able to use
 the class directly instead of a subfunction of the class... Like this..
 
 class FOO
 {
 ..?
 }
 
 FOO foo = new FOO();
 foo = 5; // See how I can just give a numeric value to it
 float bar = 5;
 foo += bar; // And interact with other types
 // foo now equals 10
 
 Is this possible? I guess I want to make an int-like class. How do you do this?
 
 Thanks,
 Trevor Parscal

I'd with the proper OO thing and use: # foo.assign( 5 );
Dec 31 2005