Perl Type Issues

Perl is a language with WeakTypeIssues.

In Perl there are is one single value type, the scalar. A scalar can represent a string, an integer or a double, and it is implementation uses these C types. But from Perl you can't tell which one it is using. Perl switches the format based on the usage context. For comparison of values, Perl has two sets of operators; string and numeric:

  • eq, ne, gt, lt, etc
  • ==, !=, >, <

DaveThomas posted a fit table to the fit-dev mailing list that demonstrates type ambiguity.

a b plus  
1 2 4 or should it be 4.0?
x y xy concatenation vs addition

Here's how I resolve it in the AlternatePerlImplementation:

    package Plusser;
    use base 'Test::FIT::ColumnFixture';

sub a { my ($self, $value) = @_; $self->{a} = $value; return; # no return value }

sub b { my ($self, $value) = @_; # Alternate way to get value $self->{b} = $self->cell->value; return; # no return value }

sub plus { my ($self, $expected) = @_; # Is value numeric? if ($self->{a} =~ /^-?[\d]+(\.\d*)?$/) { my $actual = $self->{a} + $self->{b}; if ($actual == $expected) { $self->pass; } else { $self->fail("$expected (expected) - $actual (actual)"); } } else { my $actual = $self->{a} . $self->{b}; if ($actual eq $expected) { $self->pass; } else { $self->fail("$expected (expected) - $actual (actual)"); } } return; # no return value }


This demonstrates that I have a high level of control in my fixture, and am able to do the right thing no matter what my situation. But this is terribly verbose.

Fortunately I can make this much cleaner by upstreaming all the generic code into my base class. Here's the shorter revision:

    package Plusser;
    use base 'Test::FIT::ColumnFixture';
    use Test::FIT qw(attribute);

attribute 'a'; attribute 'b';

sub plus { my ($self) = @_; if ($self->a =~ /^-?[\d]+(\.\d*)?$/) { $self->eq_num($self->a + $self->b); } else { $self->eq_str($self->a . $self->b); } }


This is about as clean as I can get it, and still retain the control I need.

Actually if 'a' and 'b' were 'x' and 'y', I could omit them because I keep a general purpose 'x', 'y', and 'z' in my base class since they come up often :)


Last edited April 21, 2003
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