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digitalmars.D - typeof headache

reply "Dan Williams" <dnews ithium.NOSPAM.net> writes:
I'm having a little trouble with typeof().

The D documentation says: "Typeof is a way to specify a type based on the
type of an expression."

That's fair enough, but in that case how do you DETECT the current type of
an expression?

I was hoping that either typeof would return something to tell me a current
type, or that I could at the very least to typeof comparison checking such
as if (typeof('c') == typeof(int)) - something like that in any case.

However, the compiler keeps yelling that it expects a dot, and I'm really
not sure how to do what I want. Things like typeof(a).sizeof work fine (by
the way, why was size deprecated in favour of sizeof? To my mind, size is
more fitting for a property, i.e. a.size, and sizeof for a function, i.e.
sizeof(a). But never mind...) however the code examples on the D site are
very sparse when it comes to typeof(), and some do not actually work at all.

I guess I'm a little confused about the purpose of typeof(), as my initial
logical assumption would be that it would check what type something is, and
yet the documentation (keyword: "specify") makes me think that it's actually
more like cast().

Which brings me to two questions: if typeof() is actually like cast(), why
is it there? And how can I detect the type of a variable (or expression)?

Sorry if this is a stupid question, but a search of the D newsgroups and a
Google of the site did not reveal anything to help me.
Jun 30 2004
next sibling parent "Dan Williams" <dnews ithium.NOSPAM.net> writes:
Thinking about it I expect someone will say at some point something like, "D
is statically typed, therefore you know the type of all variables already,
so why do you need to detect the type?"

So I'll quickly point out that in the case of a union or something you may
not always know what data type is in use, and typeof would be very useful
there. There are other cases too where you may not actually know the data
type of a variable.

I propose something like a type or typeof property, i.e. a.type or a.typeof,
just like there is a.sizeof.

Unless there's a better way to do this?



"Dan Williams" <dnews ithium.NOSPAM.net> wrote in message
news:cbu8rc$2rkn$1 digitaldaemon.com...

 I'm having a little trouble with typeof().

 The D documentation says: "Typeof is a way to specify a type based on the
 type of an expression."

 That's fair enough, but in that case how do you DETECT the current type of
 an expression?

 I was hoping that either typeof would return something to tell me a


current

 type, or that I could at the very least to typeof comparison checking such
 as if (typeof('c') == typeof(int)) - something like that in any case.

 However, the compiler keeps yelling that it expects a dot, and I'm really
 not sure how to do what I want. Things like typeof(a).sizeof work fine (by
 the way, why was size deprecated in favour of sizeof? To my mind, size is
 more fitting for a property, i.e. a.size, and sizeof for a function, i.e.
 sizeof(a). But never mind...) however the code examples on the D site are
 very sparse when it comes to typeof(), and some do not actually work at


all.

 I guess I'm a little confused about the purpose of typeof(), as my initial
 logical assumption would be that it would check what type something is,


and

 yet the documentation (keyword: "specify") makes me think that it's


actually

 more like cast().

 Which brings me to two questions: if typeof() is actually like cast(), why
 is it there? And how can I detect the type of a variable (or expression)?

 Sorry if this is a stupid question, but a search of the D newsgroups and a
 Google of the site did not reveal anything to help me.
Jun 30 2004
prev sibling next sibling parent reply "me" <memsom interalpha.co.uk> writes:
 I was hoping that either typeof would return something to tell me a


current

 type, or that I could at the very least to typeof comparison checking such
 as if (typeof('c') == typeof(int)) - something like that in any case.


I suggest that D could addopt the less ambiguous (and less prone to error)
'is' operator.

e.g

class Y {}

class X : Y {}

X x = new X();
Y y = new Y();

if (x is y) ..; //x is either a 'Y' or descends from it - they are under the
same branch of the inheritence tree

this works equally well for types

if (x is X) ...; //as before, is either of that type or a descendent

I guess you could d-ify it to :

if (x typeof y) ..;

but to my eyes that is less readable.
Jun 30 2004
next sibling parent "Dan Williams" <dnews ithium.NOSPAM.net> writes:
Hmmmm, an 'is' operator. Yes, that might work... but would it allow
something like:

if (a is int)

etc.

With typeof(), I would envisage something like;

if (typeof(a) == int)
if (typeof(a) == some_constant_meaning_int)
if (typeof(a) == typeof(int))

...that kind of thing.

But maybe an effective solution is to combine your 'is' operator with my
idea for a typeof property:

if (a.is(int))

that is admittedly not as readable/semantic as (a is int) however it would
not require any extra operators. Of course, the problem is that 'is' then
becomes a method and not a property, which is undesirable.

Personally I think either (a is int) or a.type are the best options
(probably a.typeof rather than a.type seeing as that seems to be the style
for D).



"me" <memsom interalpha.co.uk> wrote in message
news:cbu9ta$2v9p$1 digitaldaemon.com...

 I was hoping that either typeof would return something to tell me a


 current

 type, or that I could at the very least to typeof comparison checking




such

 as if (typeof('c') == typeof(int)) - something like that in any case.


 I suggest that D could addopt the less ambiguous (and less prone to error)
 'is' operator.

 e.g

 class Y {}

 class X : Y {}

 X x = new X();
 Y y = new Y();

 if (x is y) ..; //x is either a 'Y' or descends from it - they are under


the

 same branch of the inheritence tree

 this works equally well for types

 if (x is X) ...; //as before, is either of that type or a descendent

 I guess you could d-ify it to :

 if (x typeof y) ..;

 but to my eyes that is less readable.
Jun 30 2004
prev sibling next sibling parent "Dan Williams" <dnews ithium.NOSPAM.net> writes:
I just noticed there already is an 'is' operator, so it would seem that one
is out...


"me" <memsom interalpha.co.uk> wrote in message
news:cbu9ta$2v9p$1 digitaldaemon.com...

 I was hoping that either typeof would return something to tell me a


 current

 type, or that I could at the very least to typeof comparison checking




such

 as if (typeof('c') == typeof(int)) - something like that in any case.


 I suggest that D could addopt the less ambiguous (and less prone to error)
 'is' operator.

 e.g

 class Y {}

 class X : Y {}

 X x = new X();
 Y y = new Y();

 if (x is y) ..; //x is either a 'Y' or descends from it - they are under


the

 same branch of the inheritence tree

 this works equally well for types

 if (x is X) ...; //as before, is either of that type or a descendent

 I guess you could d-ify it to :

 if (x typeof y) ..;

 but to my eyes that is less readable.
Jun 30 2004
prev sibling parent Mike Swieton <mike swieton.net> writes:
On Wed, 30 Jun 2004 12:58:34 +0100, me wrote:

 if (x is y) ..; //x is either a 'Y' or descends from it - they are under the
 same branch of the inheritence tree


That is already implemented by casts. The cast operator returns null if the
objects are unrelated:

if (cast(y) x) ...;

Mike Swieton
__
It's kind of fun to do the impossible.
	- Walt Disney
Jun 30 2004
prev sibling next sibling parent reply Norbert Nemec <Norbert.Nemec gmx.de> writes:
Did you try typeid?
----
        if(typeid(typeof(a)) == typeid(typeof(b))) ...
----

I did not try it.

I recall Walter mentioning long-term-ideas about handling types directly,
but that's certainly post-1.0




Dan Williams wrote:


 I'm having a little trouble with typeof().
 
 The D documentation says: "Typeof is a way to specify a type based on the
 type of an expression."
 
 That's fair enough, but in that case how do you DETECT the current type of
 an expression?
 
 I was hoping that either typeof would return something to tell me a
 current type, or that I could at the very least to typeof comparison
 checking such as if (typeof('c') == typeof(int)) - something like that in
 any case.
 
 However, the compiler keeps yelling that it expects a dot, and I'm really
 not sure how to do what I want. Things like typeof(a).sizeof work fine (by
 the way, why was size deprecated in favour of sizeof? To my mind, size is
 more fitting for a property, i.e. a.size, and sizeof for a function, i.e.
 sizeof(a). But never mind...) however the code examples on the D site are
 very sparse when it comes to typeof(), and some do not actually work at
 all.
 
 I guess I'm a little confused about the purpose of typeof(), as my initial
 logical assumption would be that it would check what type something is,
 and yet the documentation (keyword: "specify") makes me think that it's
 actually more like cast().
 
 Which brings me to two questions: if typeof() is actually like cast(), why
 is it there? And how can I detect the type of a variable (or expression)?
 
 Sorry if this is a stupid question, but a search of the D newsgroups and a
 Google of the site did not reveal anything to help me.
Jun 30 2004
next sibling parent reply "Bent Rasmussen" <exo bent-rasmussen.info> writes:
 Did you try typeid?
 ----
         if(typeid(typeof(a)) == typeid(typeof(b))) ...
 ----

 I did not try it.


I did

printf("%i",typeid(typeof(0)) === typeid(typeof(0)));
printf("\n%i",typeid(typeof(0)) === typeid(typeof(true)));

prints

1
0

Notice the use of the "===" operator.
Jun 30 2004
parent reply "Dan Williams" <dnews ithium.NOSPAM.net> writes:
Hmmmm, you know when using cast() you do something like:

bit a;
int b;
b = cast(int) a;

Well, I kinda assumed I could do the same with typeof/typeid/whatever?

i.e.

printf("%i",typeid(typeof(0)) === typeid(typeof(int)));

...maybe I better go play with it a bit first and see what happens :)



"Bent Rasmussen" <exo bent-rasmussen.info> wrote in message
news:cbugq2$7sv$1 digitaldaemon.com...

 Did you try typeid?
 ----
         if(typeid(typeof(a)) == typeid(typeof(b))) ...
 ----

 I did not try it.


 I did

 printf("%i",typeid(typeof(0)) === typeid(typeof(0)));
 printf("\n%i",typeid(typeof(0)) === typeid(typeof(true)));

 prints

 1
 0

 Notice the use of the "===" operator.
Jun 30 2004
parent reply "Bent Rasmussen" <exo bent-rasmussen.info> writes:
 printf("%i",typeid(typeof(0)) === typeid(typeof(int)));

 ...maybe I better go play with it a bit first and see what happens :)


If I understand this correctly typeof maps from values to types and int is
not a value, its a type, hence it doesn't make sense to use typeof on it.
Thus use

printf("%i",typeid(typeof(0)) === typeid(int));

I'm not quite sure what you're asking for.
Jun 30 2004
parent "Dan Williams" <dnews ithium.NOSPAM.net> writes:
You are correct.


"Bent Rasmussen" <exo bent-rasmussen.info> wrote in message
news:cbujou$chr$1 digitaldaemon.com...

 printf("%i",typeid(typeof(0)) === typeid(typeof(int)));

 ...maybe I better go play with it a bit first and see what happens :)


 If I understand this correctly typeof maps from values to types and int is
 not a value, its a type, hence it doesn't make sense to use typeof on it.
 Thus use

 printf("%i",typeid(typeof(0)) === typeid(int));

 I'm not quite sure what you're asking for.
Jun 30 2004
prev sibling next sibling parent "Dan Williams" <dnews ithium.NOSPAM.net> writes:
Gah... typeid? I'll have to go and look that up and play with it. I
certainly didn't know there even *was* a typeid!

Anyhow... I think the comments that have been made about typeof remain
valid.




"Norbert Nemec" <Norbert.Nemec gmx.de> wrote in message
news:cbue48$3eu$1 digitaldaemon.com...

 Did you try typeid?
 ----
         if(typeid(typeof(a)) == typeid(typeof(b))) ...
 ----

 I did not try it.

 I recall Walter mentioning long-term-ideas about handling types directly,
 but that's certainly post-1.0




 Dan Williams wrote:


 I'm having a little trouble with typeof().

 The D documentation says: "Typeof is a way to specify a type based on




the

 type of an expression."

 That's fair enough, but in that case how do you DETECT the current type




of

 an expression?

 I was hoping that either typeof would return something to tell me a
 current type, or that I could at the very least to typeof comparison
 checking such as if (typeof('c') == typeof(int)) - something like that




in

 any case.

 However, the compiler keeps yelling that it expects a dot, and I'm




really

 not sure how to do what I want. Things like typeof(a).sizeof work fine




(by

 the way, why was size deprecated in favour of sizeof? To my mind, size




is

 more fitting for a property, i.e. a.size, and sizeof for a function,




i.e.

 sizeof(a). But never mind...) however the code examples on the D site




are

 very sparse when it comes to typeof(), and some do not actually work at
 all.

 I guess I'm a little confused about the purpose of typeof(), as my




initial

 logical assumption would be that it would check what type something is,
 and yet the documentation (keyword: "specify") makes me think that it's
 actually more like cast().

 Which brings me to two questions: if typeof() is actually like cast(),




why

 is it there? And how can I detect the type of a variable (or




expression)?

 Sorry if this is a stupid question, but a search of the D newsgroups and




a

 Google of the site did not reveal anything to help me.
Jun 30 2004
prev sibling parent reply "Dan Williams" <dnews ithium.NOSPAM.net> writes:
Ok I've been and tested this typeid thing. I know C has typeid, but because
D has typeof I wasn't really expecting typeid and forgot about it.

Now, in C you can use typeid on an expression, but in D that confusingly
does not appear to be the case.

typeid(1)             fails.
typeid(typeof(1))     works.
typeid(int)           works.

so... I can do:

if (typeid(typeof(1)) == typeid(typeof(0)))...

...just as was suggested, and so too can I do:

if (typeid(typeof(1)) == typeid(int))...

But I cannot do:

if (typeof(1) == int)...

Surely this is more convoluted than it needs to be? As I see it, a lot of
this is overkill.

If typeof returns something that equates to an actual type, can we not use
that ourselves? I mean, typeid(typeof(0))) is the same as typeid(int)),
which means that typeof(0) is int, as expected, but it cannot be used like
that. Strange.

So I tried this:

printf("%d\n", typeid(typeof('c'))); // prints 4257264
printf("%d\n", typeid(typeof(1)));   // prints 4257408
printf("%d\n", typeid(int));         // prints 4257408

It would appear, therefore, that some constants are being used, but I cannot
find reference to them and do not know what they would be called.

The flaw in this theory is that:

if (typeid(typeof(1)) == 4257408)

fails miserably. It would appear that objects are being used somewhere for
some reason, so I give up.

Does this mean that I *have* to use (typeid(typeof(a)) == typeid(int)), or
is there an alternative method?



"Norbert Nemec" <Norbert.Nemec gmx.de> wrote in message
news:cbue48$3eu$1 digitaldaemon.com...

 Did you try typeid?
 ----
         if(typeid(typeof(a)) == typeid(typeof(b))) ...
 ----

 I did not try it.

 I recall Walter mentioning long-term-ideas about handling types directly,
 but that's certainly post-1.0




 Dan Williams wrote:


 I'm having a little trouble with typeof().

 The D documentation says: "Typeof is a way to specify a type based on




the

 type of an expression."

 That's fair enough, but in that case how do you DETECT the current type




of

 an expression?

 I was hoping that either typeof would return something to tell me a
 current type, or that I could at the very least to typeof comparison
 checking such as if (typeof('c') == typeof(int)) - something like that




in

 any case.

 However, the compiler keeps yelling that it expects a dot, and I'm




really

 not sure how to do what I want. Things like typeof(a).sizeof work fine




(by

 the way, why was size deprecated in favour of sizeof? To my mind, size




is

 more fitting for a property, i.e. a.size, and sizeof for a function,




i.e.

 sizeof(a). But never mind...) however the code examples on the D site




are

 very sparse when it comes to typeof(), and some do not actually work at
 all.

 I guess I'm a little confused about the purpose of typeof(), as my




initial

 logical assumption would be that it would check what type something is,
 and yet the documentation (keyword: "specify") makes me think that it's
 actually more like cast().

 Which brings me to two questions: if typeof() is actually like cast(),




why

 is it there? And how can I detect the type of a variable (or




expression)?

 Sorry if this is a stupid question, but a search of the D newsgroups and




a

 Google of the site did not reveal anything to help me.
Jun 30 2004
parent reply "Walter" <newshound digitalmars.com> writes:
typeid returns an instance of class TypeInfo corresponding to the type of
typeid's argument. For example:
    typeid(int)
returns an instance of TypeInfo corresponding to int. If two TypeInfo's
represent the same type, then their TypeInfo's will compare equal.

The reason you must do:
    typeid(typeof(0)) == typeid(int)
instead of:
    typeof(0) == int
is because of parsing ambiguities. Types and expressions follow different
grammar rules, and if there wasn't an easy way to distinguish them, it
cannot be parsed. For example:
    foo[]
is that a type array of foo's, or is it the array foo?


"Dan Williams" <dnews ithium.NOSPAM.net> wrote in message
news:cbuk8c$d8o$1 digitaldaemon.com...

 Ok I've been and tested this typeid thing. I know C has typeid, but


because

 D has typeof I wasn't really expecting typeid and forgot about it.

 Now, in C you can use typeid on an expression, but in D that confusingly
 does not appear to be the case.

 typeid(1)             fails.
 typeid(typeof(1))     works.
 typeid(int)           works.

 so... I can do:

 if (typeid(typeof(1)) == typeid(typeof(0)))...

 ...just as was suggested, and so too can I do:

 if (typeid(typeof(1)) == typeid(int))...

 But I cannot do:

 if (typeof(1) == int)...

 Surely this is more convoluted than it needs to be? As I see it, a lot of
 this is overkill.

 If typeof returns something that equates to an actual type, can we not use
 that ourselves? I mean, typeid(typeof(0))) is the same as typeid(int)),
 which means that typeof(0) is int, as expected, but it cannot be used like
 that. Strange.

 So I tried this:

 printf("%d\n", typeid(typeof('c'))); // prints 4257264
 printf("%d\n", typeid(typeof(1)));   // prints 4257408
 printf("%d\n", typeid(int));         // prints 4257408

 It would appear, therefore, that some constants are being used, but I


cannot

 find reference to them and do not know what they would be called.

 The flaw in this theory is that:

 if (typeid(typeof(1)) == 4257408)

 fails miserably. It would appear that objects are being used somewhere for
 some reason, so I give up.

 Does this mean that I *have* to use (typeid(typeof(a)) == typeid(int)), or
 is there an alternative method?



 "Norbert Nemec" <Norbert.Nemec gmx.de> wrote in message
 news:cbue48$3eu$1 digitaldaemon.com...

 Did you try typeid?
 ----
         if(typeid(typeof(a)) == typeid(typeof(b))) ...
 ----

 I did not try it.

 I recall Walter mentioning long-term-ideas about handling types




directly,

 but that's certainly post-1.0




 Dan Williams wrote:


 I'm having a little trouble with typeof().

 The D documentation says: "Typeof is a way to specify a type based on




 the

 type of an expression."

 That's fair enough, but in that case how do you DETECT the current






type

 of

 an expression?

 I was hoping that either typeof would return something to tell me a
 current type, or that I could at the very least to typeof comparison
 checking such as if (typeof('c') == typeof(int)) - something like that




 in

 any case.

 However, the compiler keeps yelling that it expects a dot, and I'm




 really

 not sure how to do what I want. Things like typeof(a).sizeof work fine




 (by

 the way, why was size deprecated in favour of sizeof? To my mind, size




 is

 more fitting for a property, i.e. a.size, and sizeof for a function,




 i.e.

 sizeof(a). But never mind...) however the code examples on the D site




 are

 very sparse when it comes to typeof(), and some do not actually work






at

 all.

 I guess I'm a little confused about the purpose of typeof(), as my




 initial

 logical assumption would be that it would check what type something






is,

 and yet the documentation (keyword: "specify") makes me think that






it's

 actually more like cast().

 Which brings me to two questions: if typeof() is actually like cast(),




 why

 is it there? And how can I detect the type of a variable (or




 expression)?

 Sorry if this is a stupid question, but a search of the D newsgroups






and

 a

 Google of the site did not reveal anything to help me.
Jun 30 2004
next sibling parent "Dan Williams" <dnews ithium.NOSPAM.net> writes:
Ahhhh, excellent, that makes sense :)

Thankyou for clearing that up!


"Walter" <newshound digitalmars.com> wrote in message
news:cbuqpf$mtp$1 digitaldaemon.com...

 typeid returns an instance of class TypeInfo corresponding to the type of
 typeid's argument. For example:
     typeid(int)
 returns an instance of TypeInfo corresponding to int. If two TypeInfo's
 represent the same type, then their TypeInfo's will compare equal.

 The reason you must do:
     typeid(typeof(0)) == typeid(int)
 instead of:
     typeof(0) == int
 is because of parsing ambiguities. Types and expressions follow different
 grammar rules, and if there wasn't an easy way to distinguish them, it
 cannot be parsed. For example:
     foo[]
 is that a type array of foo's, or is it the array foo?


 "Dan Williams" <dnews ithium.NOSPAM.net> wrote in message
 news:cbuk8c$d8o$1 digitaldaemon.com...

 Ok I've been and tested this typeid thing. I know C has typeid, but


 because

 D has typeof I wasn't really expecting typeid and forgot about it.

 Now, in C you can use typeid on an expression, but in D that confusingly
 does not appear to be the case.

 typeid(1)             fails.
 typeid(typeof(1))     works.
 typeid(int)           works.

 so... I can do:

 if (typeid(typeof(1)) == typeid(typeof(0)))...

 ...just as was suggested, and so too can I do:

 if (typeid(typeof(1)) == typeid(int))...

 But I cannot do:

 if (typeof(1) == int)...

 Surely this is more convoluted than it needs to be? As I see it, a lot




of

 this is overkill.

 If typeof returns something that equates to an actual type, can we not




use

 that ourselves? I mean, typeid(typeof(0))) is the same as typeid(int)),
 which means that typeof(0) is int, as expected, but it cannot be used




like

 that. Strange.

 So I tried this:

 printf("%d\n", typeid(typeof('c'))); // prints 4257264
 printf("%d\n", typeid(typeof(1)));   // prints 4257408
 printf("%d\n", typeid(int));         // prints 4257408

 It would appear, therefore, that some constants are being used, but I


 cannot

 find reference to them and do not know what they would be called.

 The flaw in this theory is that:

 if (typeid(typeof(1)) == 4257408)

 fails miserably. It would appear that objects are being used somewhere




for

 some reason, so I give up.

 Does this mean that I *have* to use (typeid(typeof(a)) == typeid(int)),




or

 is there an alternative method?



 "Norbert Nemec" <Norbert.Nemec gmx.de> wrote in message
 news:cbue48$3eu$1 digitaldaemon.com...

 Did you try typeid?
 ----
         if(typeid(typeof(a)) == typeid(typeof(b))) ...
 ----

 I did not try it.

 I recall Walter mentioning long-term-ideas about handling types




 directly,

 but that's certainly post-1.0




 Dan Williams wrote:


 I'm having a little trouble with typeof().

 The D documentation says: "Typeof is a way to specify a type based








on

 the

 type of an expression."

 That's fair enough, but in that case how do you DETECT the current






 type

 of

 an expression?

 I was hoping that either typeof would return something to tell me a
 current type, or that I could at the very least to typeof comparison
 checking such as if (typeof('c') == typeof(int)) - something like








that

 in

 any case.

 However, the compiler keeps yelling that it expects a dot, and I'm




 really

 not sure how to do what I want. Things like typeof(a).sizeof work








fine

 (by

 the way, why was size deprecated in favour of sizeof? To my mind,








size

 is

 more fitting for a property, i.e. a.size, and sizeof for a function,




 i.e.

 sizeof(a). But never mind...) however the code examples on the D








site

 are

 very sparse when it comes to typeof(), and some do not actually work






 at

 all.

 I guess I'm a little confused about the purpose of typeof(), as my




 initial

 logical assumption would be that it would check what type something






 is,

 and yet the documentation (keyword: "specify") makes me think that






 it's

 actually more like cast().

 Which brings me to two questions: if typeof() is actually like








cast(),

 why

 is it there? And how can I detect the type of a variable (or




 expression)?

 Sorry if this is a stupid question, but a search of the D newsgroups






 and

 a

 Google of the site did not reveal anything to help me.
Jun 30 2004
prev sibling next sibling parent reply Hauke Duden <H.NS.Duden gmx.net> writes:
Walter wrote:

 typeid returns an instance of class TypeInfo corresponding to the type of
 typeid's argument. For example:
     typeid(int)
 returns an instance of TypeInfo corresponding to int. If two TypeInfo's
 represent the same type, then their TypeInfo's will compare equal.



Hmmm. This got me thinking: how would one check if one TypeInfo instance 
represents a base class of another TypeInfo? As far as I can see no 
helpful information is included in TypeInfo.

This could be a huge problem for functions with arbitrary parameter 
lists, since then all the information you have about the type is the 
TypeInfo.

Hauke
Jun 30 2004
parent "Walter" <newshound digitalmars.com> writes:
"Hauke Duden" <H.NS.Duden gmx.net> wrote in message
news:cbus58$ots$1 digitaldaemon.com...

 Hmmm. This got me thinking: how would one check if one TypeInfo instance
 represents a base class of another TypeInfo? As far as I can see no
 helpful information is included in TypeInfo.


All class objects are instances of TypeClass, which is derived from
TypeInfo. In TypeClass, there's a member info giving the .classinfo of the
class.


 This could be a huge problem for functions with arbitrary parameter
 lists, since then all the information you have about the type is the
 TypeInfo.

 Hauke
Jun 30 2004
prev sibling parent reply Andy Friesen <andy ikagames.com> writes:
Walter wrote:

 typeid returns an instance of class TypeInfo corresponding to the type of
 typeid's argument. For example:
     typeid(int)
 returns an instance of TypeInfo corresponding to int. If two TypeInfo's
 represent the same type, then their TypeInfo's will compare equal.
 
 The reason you must do:
     typeid(typeof(0)) == typeid(int)
 instead of:
     typeof(0) == int
 is because of parsing ambiguities. Types and expressions follow different
 grammar rules, and if there wasn't an easy way to distinguish them, it
 cannot be parsed. For example:
     foo[]
 is that a type array of foo's, or is it the array foo?


Speaking of which, how much arm-twisting would it take to get more 
TypeInfo?  I'd like to be able to look at delegates and function 
pointers and pry their argument count/types apart. (it would be 
extremely handy for generating language bindings) TypeInfo for other 
'metatypes' like associative arrays would be greatly useful too.

(lastly, the holy grail: public methods that a given class exposes)

  -- andy
Jun 30 2004
parent "Walter" <newshound digitalmars.com> writes:
"Andy Friesen" <andy ikagames.com> wrote in message
news:cbuu7u$rpd$1 digitaldaemon.com...

 Speaking of which, how much arm-twisting would it take to get more
 TypeInfo?  I'd like to be able to look at delegates and function
 pointers and pry their argument count/types apart. (it would be
 extremely handy for generating language bindings) TypeInfo for other
 'metatypes' like associative arrays would be greatly useful too.


TypeInfo will get better.
Jun 30 2004
prev sibling parent reply Daniel Horn <hellcatv hotmail.com> writes:
I made a vector class with a static size member

strange things happened when size was actually a PROPERTY...
what should have been a compiler error turned into a runtime error...
and other strange havoc resulted when trying to use the size static member.

it's a good thing that nightmare is gone I tell ye :-) up with sizeof, 
down with size

Dan Williams wrote:

 I'm having a little trouble with typeof().
 
 The D documentation says: "Typeof is a way to specify a type based on the
 type of an expression."
 
 That's fair enough, but in that case how do you DETECT the current type of
 an expression?
 
 I was hoping that either typeof would return something to tell me a current
 type, or that I could at the very least to typeof comparison checking such
 as if (typeof('c') == typeof(int)) - something like that in any case.
 
 However, the compiler keeps yelling that it expects a dot, and I'm really
 not sure how to do what I want. Things like typeof(a).sizeof work fine (by
 the way, why was size deprecated in favour of sizeof? To my mind, size is
 more fitting for a property, i.e. a.size, and sizeof for a function, i.e.
 sizeof(a). But never mind...) however the code examples on the D site are
 very sparse when it comes to typeof(), and some do not actually work at all.
 
 I guess I'm a little confused about the purpose of typeof(), as my initial
 logical assumption would be that it would check what type something is, and
 yet the documentation (keyword: "specify") makes me think that it's actually
 more like cast().
 
 Which brings me to two questions: if typeof() is actually like cast(), why
 is it there? And how can I detect the type of a variable (or expression)?
 
 Sorry if this is a stupid question, but a search of the D newsgroups and a
 Google of the site did not reveal anything to help me.
Jun 30 2004
parent Regan Heath <regan netwin.co.nz> writes:
On Wed, 30 Jun 2004 14:17:21 -0700, Daniel Horn <hellcatv hotmail.com> 
wrote:


 I made a vector class with a static size member

 strange things happened when size was actually a PROPERTY...
 what should have been a compiler error turned into a runtime error...
 and other strange havoc resulted when trying to use the size static 
 member.

 it's a good thing that nightmare is gone I tell ye :-) up with sizeof, 
 down with size


Hmm... but say you now make a static class member called sizeof..

class A {
	static int sizeof;
}

void main() {
	A a = new A();
	printf("%d\n",a.sizeof);
}

this compiles, runs and prints "0".

Remove the "static int sizeof" and it compiles, runs and prints "4".

Should this be allowed, should it be a compiler error? I think it should.

Regan


 Dan Williams wrote:

 I'm having a little trouble with typeof().

 The D documentation says: "Typeof is a way to specify a type based on 
 the
 type of an expression."

 That's fair enough, but in that case how do you DETECT the current type 
 of
 an expression?

 I was hoping that either typeof would return something to tell me a 
 current
 type, or that I could at the very least to typeof comparison checking 
 such
 as if (typeof('c') == typeof(int)) - something like that in any case.

 However, the compiler keeps yelling that it expects a dot, and I'm 
 really
 not sure how to do what I want. Things like typeof(a).sizeof work fine 
 (by
 the way, why was size deprecated in favour of sizeof? To my mind, size 
 is
 more fitting for a property, i.e. a.size, and sizeof for a function, 
 i.e.
 sizeof(a). But never mind...) however the code examples on the D site 
 are
 very sparse when it comes to typeof(), and some do not actually work at 
 all.

 I guess I'm a little confused about the purpose of typeof(), as my 
 initial
 logical assumption would be that it would check what type something is, 
 and
 yet the documentation (keyword: "specify") makes me think that it's 
 actually
 more like cast().

 Which brings me to two questions: if typeof() is actually like cast(), 
 why
 is it there? And how can I detect the type of a variable (or 
 expression)?

 Sorry if this is a stupid question, but a search of the D newsgroups 
 and a
 Google of the site did not reveal anything to help me.






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Jun 30 2004