E.g. JSON modules try to detect the fact and keep the nature of numbers and strings, and in my talk at Glasgow, I'll show why it's the wrong approach and what a more Perlish way could be. See also my blog.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

I'm hacking a DBI abstraction, and I'm not sure about the side-effects of binding 42 vs "42" to a placeholder.

So I want to play safe and keep full control.

see also should-i-quote-numbers-in-sql

I hope that DBI handles that automatically according to the type of the column, but again I'm not sure ...

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}

It depends on the driver, see Why does DBI implicitly change integers to strings?

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

I'm hacking a DBI abstraction, and I'm not sure about the side-effects of binding 42 vs "42" to a placeholder.

Isn't irrelevant what Perl thinks of a variable's type when DB already knows/was told what the type of that column should be at create time? If DB column was declared as INT then don't quote (and possibly warn user of a type mismatch if any), else quote.

Having said that I read in Programming the Perl DBI:

It's equally simple to specify multiple bind values within one statement, since bind_ param( ) takes the index, starting from 1, of the parameter to bind the given value to. For example:

    $sth = $dbh->prepare( "
                SELECT name, location
                FROM megaliths
                WHERE name = ?
                AND mapref = ?
                AND type LIKE ?
            " );
    $sth->bind_param( 1, "Avebury" );
    $sth->bind_param( 2, $mapreference );
    $sth->bind_param( 3, "%Stone Circle%" );

You may have noticed that we haven't called the quote( ) method on the values. Bind values are passed to the database separately from the SQL statement,[50] so there's no need to "wrap up" the value in SQL quoting rules.

    [50] This is not strictly true, since some drivers emulate placeholders by doing a textual replacement of the placeholders with bind values before passing the SQL to the database. Such drivers use Perl's internal information to guess whether each value needs quoting or not. Refer to the driver documentation for more information. [emphasis mine]

I'm hacking a DBI abstraction, and I'm not sure about the side-effects of binding 42 vs "42" to a placeholder

Therefore, you need to determine whether the placeholder needs to be 42 or "42".

So I want to play safe and keep full control

Therefore, either:
1) having determined that the placeholder needs to be an integer, you provide $x + 0;
or
2) having determined that the placeholder needs to be a string, you provide "$x".

But I don't see that you would need to determine whether $x is an integer or a string.
Of course, things get a little more complex if there's a need to check the validity of the integer value, but that doesn't appear to be an issue (going by your description of the problem).

Cheers,
Rob

> E.g. JSON modules try to detect the fact and keep the nature of numbers and strings,

which solves my issue, thanks! :)

$str=encode_json( [$_[0]] ); does the trick, I only need to check if /^\[".*"\]$/ is matching.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}

See:

• detecting of scalar is string or numeric
• How can I test for the representation of an integer?
• How to check if a scalar value is numeric or string?
• How to tell apart numeric scalars and string scalars in Perl? (SO)

In your tests, you might want to add a case where both IOK and POK are set:

$ perl -MDevel::Peek -e 'my $x=0; $x eq 0 and Dump($x)'
SV = PVIV(0x1542e82) at 0x1548d10
  REFCNT = 1
  FLAGS = (IOK,POK,pIOK,pPOK)
  IV = 0
  PV = 0x1537840 "0"\0
  CUR = 1
  LEN = 10
[download]

You can use Data::Peek's DDual:

$ perl -MDP -wE'sub foo{DDumper[DDual($_[0])]};foo(42);foo("42");'
[   undef,
    42,
    undef,
    undef,
    0
    ]
[   42,
    undef,
    undef,
    undef,
    0
    ]
$ perl -MDP -wE'sub foo{DDual($_[0]);1;};foo(42);foo("42");'
IV(42)
  PV: SV_UNDEF
  IV: IV(42)
  NV: SV_UNDEF
  RV: SV_UNDEF
PV("42"\0)
  PV: PV("42"\0)
  IV: SV_UNDEF
  NV: SV_UNDEF
  RV: SV_UNDEF
[download]

my ($pv, $iv, $nv, $rv, $hm) = DDual ($var [, $getmagic])
[download]

Great!

Thanks Tina! :)

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}

See chocolateboy's response in "How to tell apart numeric scalars and string scalars in Perl?"

use autobox::universal qw(type);

say type("42");  # STRING
say type(42);    # INTEGER
say type(42.0);  # FLOAT 
say type(undef); # UNDEF
[download]

I want to find out if a function is called with an integer or a string containing an integer.

The best solution is to stop wanting that.

Generally speaking, a function which expects a number shouldn't care whether the number was supplied as a string or not, and a function which expects a string shouldn't care if you neglected to wrap a numeric-looking string in the proper quote marks.

If your function can be given either a number or a string and is supposed to do different things with each, consider rewriting it into two different functions, so the caller can choose which behaviour they want.

I somehow agree with you, but I didn't design SQL and have the general desire to warn my user about such glitches.

And if this dogma was generally true, this would mean that Data::Dumper was mis-designed.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}

SQL is typed, each column has a type, each function's return value has a type.

Data::Dumper tries to do the impossible. I've just finished the first part of my slides for Glasgow, they show the problems with various JSON modules, how their results are different in corner cases, how their versions differ in what they return, and how the same version could return different results under different Perl versions. You've chosen a long, dark, and distressful path.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

Another solution, which IMHO is a little more elegant than having to parse the output of another module: Scalar::Util's isdual() will return true for a scalar that has both a number and string representation. As documented, this is true for a number used in string context and the reverse for a string.

So a scalar is a number if it becomes dual after stringification, and is a string if it becomes dual after numification (and is a trap if already dual to begin with ;-) ).

perl -MScalar::Util=isdual -E "@v = (0, 1, 2, '3', '4', '5'); push @v,
+ @v; push @v, $v[0].$v[3]; push @v, $v[1]+$v[4]; isdual($_) and say f
+or @v"
0
4
[download]

Do I misunderstand the question or will the following not work?

Edit: Ok, I misunderstand the nature of the problem as noted by LanX in Re^2: Distiguishing arguments: number-strings vs real integer... My apologies.

#!/usr/bin/perl
use strict;
use warnings;
#use Data::Dump qw/pp dd/;

#use Scalar::Util qw/looks_like_number/;
#use Devel::Peek;

sub is_string {
    my $arg = $_[0];
    warn "$arg looks like number \n$&\n\n\n"
      if $arg =~ /(\d+)/;
}


is_string(1);
is_string("42");

my $n=1;
my $s="42";
my $s1="this contains the number 143";
my $s2 = "Awierd123number";

is_string($n);
is_string($s);
is_string($s1);
is_string($s2);

$n.="";                                 # cast to string
$s+=0;                                    # cast to number
is_string($n);
is_string($s);
[download]

> Do I misunderstand the question ...

I'm afraid you are. :)

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}