NAME

FP::Struct - classes for functional perl

SYNOPSIS

    use FP::Predicates qw(is_array maybe);

    use FP::Struct 'FPStructExample::Foo'=>
            ["name", # accept any value
             [maybe (\&is_array), "animals"], # accept arrays or undef
            ]
            # => "Baz", "Buzz" # optional superclasses
             ;

    # creates a constructor new that takes positional arguments and
    # copies them to a hash with the keys "name" and "animals". Also,
    # sets @Bar::ISA to ("Baz", "Buzz") if the '#' is removed. [ ] around
    # "Baz", "Buzz" are optional.  If an array is given as a field
    # declaration, then the first entry is a predicate that receives the
    # value in question, if it doesn't return true then an exception is
    # thrown.

    is( new FPStructExample::Foo ("Tim")->name, "Tim" );
    eval {
         new FPStructExample::Foo ("Tim", 0)
    };
    like $@, qr/^unacceptable value for field 'animals': 0 /;
    is (new FPStructExample::Foo (undef, ["Struppi"])->animals->[0], "Struppi");
    is (new_ FPStructExample::Foo (animals=> ["Struppi"])->animals->[0], "Struppi");


    # Usually preferred alternative: define the struct from within the
    # package:

    # a mixin package, if this weren't defined at the time of 'use
    # FP::Struct' below, it would try to load Hum.pm
    package FPStructExample::Hum {
        sub hum {
            my $s=shift;
            $s->name." hums ".$s->a." over ".$s->b
        }
    }
    package FPStructExample::Hah {
        use FP::Struct ["aa"];
        _END_
    }

    package FPStructExample::Bar2 {

      use Chj::TEST; # the TEST sub will be removed from the package upon
                     # _END_ (namespace cleaning)
      use FP::Struct ["a","b"]=> "FPStructExample::Foo",
                                 "FPStructExample::Hum",
                                 "FPStructExample::Hah";
      sub div {
         my $s=shift;
         $$s{a} / $$s{b}
      }
      TEST { FPStructExample::Bar2->new_(a=> 1, b=> 2)->div } 1/2;
      _END_ # generate accessors for methods of given name which don't
            # exist yet *in either Bar or any super class*. (Does that
            # make sense?)
    }

    my $bar= new FPStructExample::Bar2 ("Franz", ["Barney"], "some aa", 1,2);
    # same thing, but with sub instead of method call interface:
    my $baz= FPStructExample::Bar2::c::Bar2 ("Franz", ["Barney"], "some aa", 1,2);
    # or:
    import FPStructExample::Bar2::constructors;
    my $baz= Bar2 ("Franz", ["Barney"], "some aa", 1,2);

    is $bar->div, 1/2;

    is(Bar2_(a=>1,b=>2)->div, 1/2);
    is(FPStructExample::Bar2::c::Bar2_(a=>1, b=>2)->div, 1/2);
    is(new__ FPStructExample::Bar2({a=>1,b=>2})->div, 1/2);
    is(unsafe_new__ FPStructExample::Bar2({a=>1,b=>2})->div, 1/2);
    # NOTE: unsafe_new__ returns the argument hash after checking and
    # blessing it, it doesn't copy it! Be careful. `new__` does copy it.

    is $bar->b_set(3)->div, 1/3;

    use FP::Div 'inc';
    is $bar->b_update(\&inc)->div, 1/3;

    is $bar->hum, "Franz hums 1 over 2";

    is Chj::TEST::run_tests("FPStructExample::Bar2")->success, 1;
    is (FPStructExample::Bar2->can("TEST"), undef);
    # ^ it was removed by namespace cleaning

DESCRIPTION

Create functional setters (i.e. setters that return a copy of the object so as to leave the original unharmed), take predicate functions (not magic strings) for dynamic type checking, simpler than Class::Struct.

Also creates constructor methods: `new` that takes positional arguments, `new_` which takes name=> value pairs, `new__` which takes a hash with name=> value pairs as a single argument, and `unsafe_new__` which does the same as `new__` but reuses the given hash (unsafe if the latter is modified later on).

Also creates constructor functions (i.e. subroutine instead of method calling interface) `Foo::Bar::c::Bar()` for positional and `Foo::Bar::c::Bar_()` for named arguments for package Foo::Bar. These are also in `Foo::Bar::constructors::` and can be imported using (without arguments, it imports both):

    import Foo::Bar::constructors qw(Bar Bar_);

_END_ does namespace cleaning: any sub that was defined before the use FP::Struct call is removed by the _END_ call (those that are not the same sub ref anymore, i.e. have been redefined, are left unchanged). This means that if the 'use FP::Struct' statement is put after any other (procedure-importing) 'use' statement, but before the definition of the methods, that the imported procedures can be used from within the defined methods, but are not around afterwards, i.e. they will not shadow super class methods. (Thanks to Matt S Trout for pointing out the idea.) To avoid the namespace cleaning, write _END__ instead of _END_.

See FP::Predicates for some useful predicates (others are in the respective modules that define them, like `is_pair` in `FP::List`).

PURITY

FP::Struct uses `FP::Abstract::Pure` as default base class (i.e. when no other base class is given). This means objects from classes based on FP::Struct are automatically treated as pure by `is_pure` from `FP::Predicates`.

To hold this promise true, your code must not mutate any object fields except when it's impossible for the outside world to detect (e.g. using a hash key to hold a cached result is fine as long as you also override all the functional setters for fields that are used for the calculation of the cached value to clean the cache (TODO: provide option to turn off generation of setters, and/or provide hook (for cloning?)).)

ALSO SEE

<FP::Struct::Show>

NOTE

This is alpha software! Read the status section in the package README or on the website.