Simplify the invocation of a common method

Question

I have a class like this:

class Foo {
    method some-method(Str $name) { ... }
}

Simple usage:

my $foo = Foo.new;

$foo.some-method("peter");

Since the "some-method" will be called quite frequently, I'd like to do something to allow users to use it like below:

$foo.peter;

I know FALLBACK will do the job, but it has been used for another method. I tried to define an infix operator:

sub infix:<%>(Foo $foo, $name) {
    $foo.some-method($name);
}

The code below works, but the double quote is annoying.

$foo % "peter";

So is there any way to avoid the quote mark? Or any way to simplify the invocation?

Answer 1

As Curt Tilmes already pointed out, you could make your Foo object act as an Associative (or Hash):

class Foo {
    method some-method(Str $name) { ... }
    method AT-KEY(Str $name) { self.some-method($name) }
}
my $foo = Foo.new;
say $foo<peter>;   # same as $foo.some-method("peter")

Of course, the AT-KEY method can be a multi, so you could play all sorts of tricks with that as well.

class Foo {
    method some-method(Str $name) { "$name is ok" }
    multi method AT-KEY("peter")   { "peter is special" }
    multi method AT-KEY(Str $name) { self.some-method($name) }
}
my $foo = Foo.new;
say $foo<peter>;   # "peter is special"
say $foo<joe>;     # "joe is ok"

Answer 2

There is a way that you can use FALLBACK for more than one operation, provided they are different in some way.

• By checking some property of the object:

  class Foo {
    # this could be set as part of `new`/`BUILD`
    has %!special = ( "peter" => 42 );
  
    multi method FALLBACK ( $name where (%!special{$name}:exists) ) {
      %!special{$name}
    }
  
    multi method FALLBACK ( $other ) {
      $other.tc
    }
  }
  
  with Foo.new {
    say .paul; # Paul
    say .peter; # 42
  }
  

  This has the potential problem of action-at-a-distance.

• With different number or types of arguments:

  class Bar {
    multi method FALLBACK ( Str:D $name ) {
      $name.tc
    }
    multi method FALLBACK ( Str:D $name, Real:D $number ) {
      $name.tc, 1 / $number
    }
    multi method FALLBACK ( Str:D $name, Str:D $other ) {
      $name.tc, $other.uc
    }
  }
  
  with Bar.new {
    say .paul;          # Paul
    say .peter(42);     # Peter, 0.02381
    say .peter('Paul'); # Peter, PAUL
  }
  

---

You can use .[…] for an Int argument.

class Baz {
  method AT-POS ( $arg ) { say "Baz[$arg]" }
}
Baz.new[42,32]; # Baz[42]
                # Baz[32]

The built-in postcircumfix:« [ ] » coerces the arguments to Int, but you could add a new one into the mix.
(There are a bunch of caveats with doing this.)

multi sub postcircumfix:<[ ]> ( Baz:D $b, $a ) is export {
  # $b.AT-POS( $a )

  $b.some-method( $a )
}

---

You can use .<…> for space separated Strs or .{…} for arbitrary values.

class Other {
  multi method AT-KEY ( Str:D $name ){
    $name.tc
  }
  multi method AT-KEY ( Real:D $number ){
    1 / $number
  }
}

with Other.new {
  say $_<peter>;     # Peter
  say $_.<paul>;     # Paul
  say .<peter paul>; # Peter Paul
  # note that AT-Key got called twice

  say $_{42,'peter'}; # 0.02381, Peter
  # note that AT-Key got called twice
}

---

You can make it so that your object is callable.

class Fubar {
  multi method CALL-ME ( Str:D $name ){
    $name.tc
  }
  multi method CALL-ME ( Real:D $number ){
    1 / $number
  }
  multi method CALL-ME ( +@args ){
    @args.map: {self.CALL-ME($_)}
  }
}

with Fubar.new {
  say $_('peter');   # Peter
  say $_(42);        # 0.02381

  # this calls the +@args one
  say $_('paul',32); # Paul, 0.03125
}

---

You should really think about your API before doing any of these.