Re: C#'s 'is' equivalent in D
On Thursday, 10 October 2019 at 16:33:47 UTC, H. S. Teoh wrote:
On Thu, Oct 10, 2019 at 03:58:02PM +, jmh530 via
Digitalmars-d-learn wrote:
On Thursday, 10 October 2019 at 15:47:58 UTC, Just Dave wrote:
> In C# you can do something like:
>
>
> if (obj is Person)
> {
> var person = obj as Person;
> // do stuff with person...
> }
[...]
You mean something like below:
class Person {
int id;
this(int x) {
id = x;
}
}
void main() {
auto joe = new Person(1);
if (is(typeof(joe) == Person)) {
assert(joe.id == 1);
}
}
Unfortunately, typeof is a compile-time construct, so this will
not work if you're receiving a Person object via a base class
reference. The correct solution is to cast the base class to
the derived type, which will yield null if it's not an instance
of the derived type.
T
Ah, you mean something like below:
class Person {
int id;
this(int x) {
id = x;
}
}
class Employee : Person {
int job_id;
this(int x, int y) {
super(x);
job_id = y;
}
}
void main() {
import std.stdio : writeln;
Person joe = new Employee(1, 2);
if (is(typeof(joe) == Employee)) {
writeln("here"); //not called in this case
}
}
Re: C#'s 'is' equivalent in D
On Thu, Oct 10, 2019 at 03:58:02PM +, jmh530 via Digitalmars-d-learn wrote:
> On Thursday, 10 October 2019 at 15:47:58 UTC, Just Dave wrote:
> > In C# you can do something like:
> >
> >
> > if (obj is Person)
> > {
> > var person = obj as Person;
> > // do stuff with person...
> > }
[...]
> You mean something like below:
>
> class Person {
> int id;
> this(int x) {
> id = x;
> }
> }
>
> void main() {
> auto joe = new Person(1);
> if (is(typeof(joe) == Person)) {
> assert(joe.id == 1);
> }
> }
Unfortunately, typeof is a compile-time construct, so this will not work
if you're receiving a Person object via a base class reference. The
correct solution is to cast the base class to the derived type, which
will yield null if it's not an instance of the derived type.
T
--
LINUX = Lousy Interface for Nefarious Unix Xenophobes.
Re: C#'s 'is' equivalent in D
On Thursday, 10 October 2019 at 15:47:58 UTC, Just Dave wrote:
In C# you can do something like:
if (obj is Person)
{
var person = obj as Person;
// do stuff with person...
}
where you can check the type of an object prior to casting.
Does D have a similar mechanism? It's so widely useful in the
C# realm that they even added syntactic sugar to allow:
if (obj is Person person)
{
// do stuff with person...
}
I would presume since D has reference objects there must exist
some mechanism for this...
You mean something like below:
class Person {
int id;
this(int x) {
id = x;
}
}
void main() {
auto joe = new Person(1);
if (is(typeof(joe) == Person)) {
assert(joe.id == 1);
}
}
Re: C#'s 'is' equivalent in D
On Thursday, 10 October 2019 at 15:53:20 UTC, Adam D. Ruppe wrote:
On Thursday, 10 October 2019 at 15:47:58 UTC, Just Dave wrote:
if (obj is Person person)
Looks the same as D's
if(auto person = cast(Person) obj) {
// use person in here
} else {
// it was some other type
}
Excellent!
Re: C#'s 'is' equivalent in D
On Thursday, October 10, 2019 9:47:58 AM MDT Just Dave via Digitalmars-d-
learn wrote:
> In C# you can do something like:
>
>
> if (obj is Person)
> {
> var person = obj as Person;
> // do stuff with person...
> }
>
> where you can check the type of an object prior to casting. Does
> D have a similar mechanism? It's so widely useful in the C# realm
> that they even added syntactic sugar to allow:
>
> if (obj is Person person)
> {
> // do stuff with person...
> }
>
> I would presume since D has reference objects there must exist
> some mechanism for this...
D's solution is basically the same as C++'s solution. You cast and then
check whether the result is null. So,
if(cast(Person)obj !is null)
{
}
or since using a pointer or reference in an if condition checks whether it's
null or not
if(cast(Person)obj)
{
}
and you can even declare a variable that way if you want. e.g.
if(auto person = cast(Person)obj)
{
}
When D's is is used to compare two objects, it checks whether they're equal
bitwise. So, it's typically used for comparing pointers or references for
equality (whereas using == with references would compare the objects
themselves for equality).
- Jonathan M Davis
Re: C#'s 'is' equivalent in D
On 10/10/19 6:47 PM, Just Dave wrote:
In C# you can do something like:
if (obj is Person)
{
var person = obj as Person;
// do stuff with person...
}
where you can check the type of an object prior to casting. Does D have
a similar mechanism? It's so widely useful in the C# realm that they
even added syntactic sugar to allow:
if (obj is Person person)
{
// do stuff with person...
}
I would presume since D has reference objects there must exist some
mechanism for this...
```D
if (auto person = cast(Person) obj)
{
// do stuff with person...
}
```
Re: C#'s 'is' equivalent in D
On Thursday, 10 October 2019 at 15:47:58 UTC, Just Dave wrote:
if (obj is Person person)
Looks the same as D's
if(auto person = cast(Person) obj) {
// use person in here
} else {
// it was some other type
}
Re: C#'s 'is' equivalent in D
Even though static solutions would be more performance minded, I'd actually prefer to see the runtime equivalent so I don't have to rethink how I think as performance isn't really my major concern right now.
