dynamic object creation

[Aryeh Friedman]

If I have something like this:

s="Array"

How whould I get something like this:

aObject=s.new

In "plain" english I am asking if I have a valid name of a class in a
string how do I create an instance of the class the string contains?

[Simon Strandgaard]

On Mon, 30 Jun 2003 16:49:05 +0000, Aryeh Friedman wrote:

> If I have something like this:
>
> s="Array"
>
> How whould I get something like this:
>
> aObject=s.new
>
> In "plain" english I am asking if I have a valid name of a class in a
> string how do I create an instance of the class the string contains?

How about this ?

s="Array"
aObject=eval(s+".new")


--
Simon Strandgaard

[stefano]

On Mon, 30 Jun 2003 15:49:05 +0000, Aryeh Friedman wrote:

> If I have something like this:
>
> s="Array"
>
> How whould I get something like this:
>
> aObject=s.new
>
> In "plain" english I am asking if I have a valid name of a class in a
> string how do I create an instance of the class the string contains?

s = "Array"
aObject = eval(s).new

--
ste

[Brian Candler]

On Tue, Jul 01, 2003 at 01:22:22AM +0900, stefano wrote:

> On Mon, 30 Jun 2003 15:49:05 +0000, Aryeh Friedman wrote:
>

> > If I have something like this:
> >
> > s="Array"
> >
> > How whould I get something like this:
> >
> > aObject=s.new
> >
> > In "plain" english I am asking if I have a valid name of a class in a
> > string how do I create an instance of the class the string contains?

>
> s = "Array"
> aObject = eval(s).new

... and just hope nobody passes in s = "`rm -rf /*`" as a class name :-|

const_get will be much faster too, as it doesn't have to compile a piece of
code each time.

[Dave Thomas]

John Platte wrote:

> On the page you referenced, the entry for const_defined? says it takes a
> symbol too, but the example code uses a string argument...!? Same for
> const_set.

>> I just tested it and to my surprise it worked?!
>>
>> [url]http://rubycentral.com/book/ref_c_module.html#Module.const_get[/url]
>>
>> says that I need to supply a symbol, why does it accept a string?

At the top of the section, you'll find "In the descriptions that follow,
the parameter aSymbol refers to a symbol, which is either a quoted
string or a Symbol (such as :name)."

Cheers


Dave

[John Platte]

[url]http://rubycentral.com/book/ref_c_module.htm[/url]

I spoke too soon. At the top of the page:

> In the descriptions that follow, the parameter aSymbol refers to a
> symbol, which is either a quoted string or a Symbol (such as :name )

Sorry for the spurious post.

On Monday, Jun 30, 2003, at 15:33 America/Chicago, John Platte wrote:

> On the page you referenced, the entry for const_defined? says it takes
> a symbol too, but the example code uses a string argument...!? Same
> for const_set.
>
> On Monday, Jun 30, 2003, at 15:23 America/Chicago, Anders Borch wrote:
>

>>> A class name is just a constant, so something like
>>> a = Module.const_get("Array").new

>>
>> uhm... why does this work?
>>
>> I just tested it and to my surprise it worked?!
>>
>> [url]http://rubycentral.com/book/ref_c_module.html#Module.const_get[/url]
>>
>> says that I need to supply a symbol, why does it accept a string?
>>
>> is this something that will continue to work in 1.8? (im still using
>> 1.6.8 on my winbox and 1.6.7 on my linux box)

--
John Platte
Principal Consultant, NIKA Consulting
[url]http://nikaconsulting.com/[/url]
(630) 499 9830
Fax: (630) 566 0655

[Anders Borch]

Brian Candler wrote:

> On Tue, Jul 01, 2003 at 01:01:25AM +0900, Aryeh Friedman wrote:
>

>>If I have something like this:
>>
>>s="Array"
>>
>>How whould I get something like this:
>>
>>aObject=s.new
>>
>>In "plain" english I am asking if I have a valid name of a class in a
>>string how do I create an instance of the class the string contains?

>
>
> A class name is just a constant, so something like
>
> a = Module.const_get("Array").new

uhm... why does this work?

I just tested it and to my surprise it worked?!

[url]http://rubycentral.com/book/ref_c_module.html#Module.const_get[/url]

says that I need to supply a symbol, why does it accept a string?

is this something that will continue to work in 1.8? (im still using
1.6.8 on my winbox and 1.6.7 on my linux box)

>
> is what you need (Aside: what's the proper way to access 'the top-level
> Module', or is the above correct?)
>
> Cheers,
>
> Brian.
>

--
dc -e
4dd*od3*dddn1-89danrn10-dan3+ann6*dan*2*an13dn1+dn2-dn3+5*ddan2/9+an13nap

[Anders Borch]

Dave Thomas wrote:

> John Platte wrote:
>

>> On the page you referenced, the entry for const_defined? says it takes
>> a symbol too, but the example code uses a string argument...!? Same
>> for const_set.

>
>

>>> I just tested it and to my surprise it worked?!
>>>
>>> [url]http://rubycentral.com/book/ref_c_module.html#Module.const_get[/url]
>>>
>>> says that I need to supply a symbol, why does it accept a string?

>
>
> At the top of the section, you'll find "In the descriptions that follow,
> the parameter aSymbol refers to a symbol, which is either a quoted
> string or a Symbol (such as :name)."
>

thanks alot :) I'll try to *read* from now on ;)

--
dc -e
4dd*od3*dddn1-89danrn10-dan3+ann6*dan*2*an13dn1+dn2-dn3+5*ddan2/9+an13nap

[stefano]

On Tue, 01 Jul 2003 05:01:08 +0900, Brian Candler wrote:

> .. and just hope nobody passes in s = "`rm -rf /*`" as a class name :-|

obviously, if you don't check what you're passing to eval(), you deserve
all the bad things that could happen :-)

> const_get will be much faster too, as it doesn't have to compile a piece of
> code each time.

that's true, I didn't think about it.

--
ste

[Anders Borch]

Brian Candler wrote:

> On Tue, Jul 01, 2003 at 05:23:35AM +0900, Anders Borch wrote:
>

>>>A class name is just a constant, so something like
>>>
>>> a = Module.const_get("Array").new

>>
>>uhm... why does this work?
>>
>>I just tested it and to my surprise it worked?!
>>
>>[url]http://rubycentral.com/book/ref_c_module.html#Module.const_get[/url]
>>
>>says that I need to supply a symbol, why does it accept a string?

>
>
> Even if it didn't, you can easily convert strings to symbols and vice versa.
>
> "Array".intern
> => :Array

hadn't seen that one, thanks =)

> :Array.to_s
> => "Array"
>
> Regards,
>
> Brian.
>

--
dc -e
4dd*od3*dddn1-89danrn10-dan3+ann6*dan*2*an13dn1+dn2-dn3+5*ddan2/9+an13nap

[Robert Klemme]

"Brian Candler" <B.Candler@pobox.com> schrieb im Newsbeitrag
news:20030630171414.A19372@linnet.org...

> On Tue, Jul 01, 2003 at 01:01:25AM +0900, Aryeh Friedman wrote:

> > If I have something like this:
> >
> > s="Array"
> >
> > How whould I get something like this:
> >
> > aObject=s.new
> >
> > In "plain" english I am asking if I have a valid name of a class in a
> > string how do I create an instance of the class the string contains?

>
> A class name is just a constant, so something like
>
> a = Module.const_get("Array").new
>
> is what you need (Aside: what's the proper way to access 'the top-level
> Module', or is the above correct?)

I think this does it

a = Kernel.const_get("Array").new

robert