String to Num (was Re: Numeric Literals (Summary))

[Michael Lazzaro]

Let's summarize some of the string-to-num issues:

(1) -- A number is just a number, regardless of how it's put in. Therefore:

my int $i = 0xff;
my int $i = 255;

result in the identical number, 255, being placed in $i. Once it's in there, there's no way to tell what format it originally came in, because we don't care.


(2) -- We want to be able to parse a string as a number using all the same rules that Perl uses. This implies there is a function, perhaps C<literal> or similar, that allows this:

my int $i = literal "0xff"; # 255


(3) -- We want to be able to parse a string as a number using a very _specific_ rule; for example, if a user is expected to enter a value in a specific format, like octal "755" or hex "FF", we want to "know" what we're expecting. That implies there may be functions for each common format:

my int $i = sci "1e33";
my int $i = hex "00ff";


(4) -- We want to be able to output numbers to strings according to specific formatting rules. One way to do this (aside from using sprintf) is to use sprintf-style formatting strings, perhaps as properties to tie them to individual instances:

my int $i = literal "0xff" but as_string('%02x');

or explicitly each time you call the stringifyier:

my str $s = str($i : base => 16 );
my str $s = str($i : format => '%02x');

or explicitly by using a class method of the number to force it:

my str $s = $i.as_string('%02x');


(5) -- An earlier proposal I had is to make C<bin>, C<oct>, C<hex>, etc. subclasses that overloaded their string-in and string-out methods, such that:

my sci $i = "1e5" # 10**5
my hex $i = "ff"; # 255
print $i; # "FF"
print bin $i; # "11111111"

which is very useful for some scripts, and would give the typecasts shown in (3) and (4) for free. If you wanted to do the same for any arbitrary format, you'd have to make your own classes with similar string in/out rules.

Comments?

MikeL