From Newsgroup: comp.lang.tcl

Is it possible to create class-specific consts i.e., consts that exist
inside a class's namespace?

For example, this does _not_ work:

```

oo::class create Klass {
const SPECIAL special

method say {} { return $SPECIAL }
}

set klass [Klass new]
puts "$Klass::SPECIAL [$klass say]"

```
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From Newsgroup: comp.lang.tcl

Mark Summerfield <[email protected]> wrote:

Is it possible to create class-specific consts i.e., consts that exist inside a class's namespace?

Tcl does not have "constants" in the vien of other languages
"constants".

However, there are several ways to "roll your own": https://wiki.tcl-lang.org/page/constants

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From Newsgroup: comp.lang.tcl

On Fri, 20 Jun 2025 13:28:13 -0000 (UTC), Rich wrote:

Mark Summerfield <[email protected]> wrote:

Is it possible to create class-specific consts i.e., consts that exist
inside a class's namespace?

Tcl does not have "constants" in the vien of other languages
"constants".

However, there are several ways to "roll your own": https://wiki.tcl-lang.org/page/constants

According to https://www.tcl-lang.org/man/tcl9.0/TclCmd/const.html
"const — create and initialize a constant"

And I use them quite a lot since I'm using Tcl 9.

Perhaps the wiki needs updating?
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From Newsgroup: comp.lang.tcl

Mark Summerfield <[email protected]> wrote:

On Fri, 20 Jun 2025 13:28:13 -0000 (UTC), Rich wrote:

Mark Summerfield <[email protected]> wrote:

Is it possible to create class-specific consts i.e., consts that exist
inside a class's namespace?

Tcl does not have "constants" in the vien of other languages
"constants".

However, there are several ways to "roll your own":
https://wiki.tcl-lang.org/page/constants

According to https://www.tcl-lang.org/man/tcl9.0/TclCmd/const.html
"const — create and initialize a constant"

And I use them quite a lot since I'm using Tcl 9.

Ah, it seems Tcl 9 added "const" capabilities.

Perhaps the wiki needs updating?

Indeed, that would seem to be the case.

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From Newsgroup: comp.lang.tcl

On Fri, 20 Jun 2025 20:28:25 -0000 (UTC), Rich wrote:

Mark Summerfield <[email protected]> wrote:

On Fri, 20 Jun 2025 13:28:13 -0000 (UTC), Rich wrote:

Mark Summerfield <[email protected]> wrote:

Is it possible to create class-specific consts i.e., consts that
exist inside a class's namespace?

Tcl does not have "constants" in the vien of other languages
"constants".

However, there are several ways to "roll your own":
https://wiki.tcl-lang.org/page/constants

According to https://www.tcl-lang.org/man/tcl9.0/TclCmd/const.html
"const — create and initialize a constant"

And I use them quite a lot since I'm using Tcl 9.

Ah, it seems Tcl 9 added "const" capabilities.

Perhaps the wiki needs updating?

Indeed, that would seem to be the case.

I've updated the web page https://wiki.tcl-lang.org/page/constants accordingly.
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From Newsgroup: comp.lang.tcl

On Fri, 20 Jun 2025 07:58:37 -0000 (UTC)
Mark Summerfield <[email protected]> wrote:

Is it possible to create class-specific consts i.e., consts that exist inside a class's namespace?

For example, this does _not_ work:

```

oo::class create Klass {
const SPECIAL special

method say {} { return $SPECIAL }
}

set klass [Klass new]
puts "$Klass::SPECIAL [$klass say]"

```

Maybe there are more straightforward methods, but this one works:

% oo::class create C {
method foo {} { # reads the constant
classvariable CVar
puts $CVar
}
method bar {} { # tries to set the constant
classvariable CVar
set CVar "other value"
}
}
::C
% namespace eval [info object namespace C] {
# defines the constant in the class namespace
const CVar "My class variable"
}
% C create o
::o
% o foo
My class variable
% o bar
can't set "CVar": variable is a constant


Regards
--
Emiliano
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From Newsgroup: comp.lang.tcl

On Sat, 21 Jun 2025 14:03:33 -0300
Emiliano <[email protected]d> wrote:

On Fri, 20 Jun 2025 07:58:37 -0000 (UTC)
Mark Summerfield <[email protected]> wrote:

Is it possible to create class-specific consts i.e., consts that exist inside a class's namespace?

For example, this does _not_ work:

```

oo::class create Klass {
const SPECIAL special

method say {} { return $SPECIAL }
}

set klass [Klass new]
puts "$Klass::SPECIAL [$klass say]"

```

Maybe there are more straightforward methods, but this one works:

Answering myself:

% oo::class create C {
initialize {
variable CVar
const CVar "My class variable"
}
method foo {} { # reads the constant
classvariable CVar
puts $CVar
}
method bar {} { # tries to set the constant
classvariable CVar
set CVar "other value"
}
}
::C
% C create o
::o
% o foo
My class variable
% o bar
can't set "CVar": variable is a constant


Regards
--
Emiliano
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