# New Ticket Created by Klaas-Jan Stol
# Please include the string: [perl #58252]
# in the subject line of all future correspondence about this issue.
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=58252 >
The following issues are not entirely clear from PDD19:
[1]
according to PDD19 (PIR) you can declare a .const as follows:
=item .const <type> <identifier> = <const>
Define a constant named I<identifier> of type I<type> and assign value
I<const> to it. The I<type> may be either an integer value or a string
constant. The constant is stored in the constant table of the current
bytecode file.
<type> stands for "int", "num", "string" or "pmc". However, writing "pmc"
does not make any sense, because <const> must be some literal constant, such
as 42, 3.14 or "hello"; it doesn't make sense to write:
.const pmc x = "hi" # what type will x be?
THerefore, should we allow "pmc" as a type here? I see 2 reasonable
solutions:
1: disallow "pmc" altogether
2: based on the type of the constant (int-constant, num-constant or string
constant), make the variable (eh, constant) a constant of one of the
standard types (Integer, Float or String , respectively).
[2]
you can declare a .const using a PMC class type id:
.const .Sub x = "foo"
AFAIU, type ids will be removed altogether (is this true?).
If so, then the above would be invalid.
Instead, we might allow for writing:
.const "Sub" x = "foo".
Which seems a nice enough solution, but this solution is rather limited, in
that you can't create, for instance, an Array constant:
.const "Array" a = "foo" # doesn't make sense.
I know the creation of Sub constants is useful, so we definitely should keep
something like this around.
I see the following solutions:
1: only allow pmc types that are reasonable:
- .const "Integer" x = 42
- .const "Float" PI = 3.14
- .const "String" message = "hi there"
- .const "Sub" x = "foo"
and report an error message if you would do something weird as ".const 'Env'
e = 10".
2: extend syntax for other variants, for instance, to initialize arrays and
hashtables:
- .const "Array" a = (1, 2, 3, 4) # creates a constant array with 4
elements, nrs 1 to 4
- .const "Hash" h1 = {"x"=>42, "y"=>10} ## using syntactic sugar form that
is used for named arguments as well
- .const "Hash" h2 = { 42 :named("x"), 10 :named("y") } ## to be consistent
with the above, using syntax well-known in named-arguments.
Not sure if this would be helpful/possible, but just some thoughts.
comments welcome.
kjs
