4 ms·

Show HN: Dirty-equals – Doing dirty (but useful) things with equals

25 points by scolvin 5y ago

pie_flavor 5y ago
Raku has this feature by design. While there technically is a general equality operator `eqv`, you rarely see it used. Instead, you use the matching operator, `~~`, which can check equality, or check if a string matches a regex, or check if a number is contained within a range, etc.
- lizmat 5y ago
  The operator is called "smart-match". When you do: $a ~~ $b You are in fact doing: $b.ACCEPTS($a) So any object can determine how it will interpret any other object in smart-matching. The core classes or course have all these methods implemented in the expected way. And you can easily do that for your own classes as well: class Foo { multi method ACCEPTS(Int:D $count) { $count == 42 } multi method ACCEPTS("frobnicate" --> True) { } } my $foo = Foo.new; say 42 ~~ $foo; # True say 666 ~~ $foo; # False say "what" ~~ $foo; # False say "frobnicate" ~~ $foo; # True
quietbritishjim 5y ago
assert user_data == { 'id': IsPositiveInt, 'avatar_file': IsStr(regex=r'/[a-z0-9\-]{10}/example\.png'), > Without dirty-equals, you'd have to compare individual fields and/or modify some fields before comparison ... Hmm, I'm not convinced. Why not assert dirty_check(user_data, { 'id': IsPositiveInt, 'avatar_file': IsStr(regex=r'/[a-z0-9\-]{10}/example\.png'), It would work just as well without abusing the == operator. Doing so seems like a bit of a gimmick (although the actual functionality of the library looks useful). Edit: Ah, I guess the difference is that dict.__eq__ (and list.__eq__ and so on) recursively tests equality of all child elements. So to support arbitrary nesting I think it really does have to be the equals operator.
- scolvin 5y ago
  I disagree, this is much less clear. It also don't work well with pytest's error output.
  - scolvin 5y ago
    And it would be much more complex to implement, particularly with recursively nested types.
high_byte 5y ago
this is pretty neat!

25 points by scolvin 5y ago

Raku has this feature by design. While there technically is a general equality operator `eqv`, you rarely see it used. Instead, you use the matching operator, `~~`, which can check equality, or check if a string matches a regex, or check if a number is contained within a range, etc.

lizmat 5y ago
The operator is called "smart-match". When you do: $a ~~ $b You are in fact doing: $b.ACCEPTS($a) So any object can determine how it will interpret any other object in smart-matching. The core classes or course have all these methods implemented in the expected way. And you can easily do that for your own classes as well: class Foo { multi method ACCEPTS(Int:D $count) { $count == 42 } multi method ACCEPTS("frobnicate" --> True) { } } my $foo = Foo.new; say 42 ~~ $foo; # True say 666 ~~ $foo; # False say "what" ~~ $foo; # False say "frobnicate" ~~ $foo; # True

quietbritishjim 5y ago

assert user_data == { 'id': IsPositiveInt, 'avatar_file': IsStr(regex=r'/[a-z0-9\-]{10}/example\.png'), > Without dirty-equals, you'd have to compare individual fields and/or modify some fields before comparison ... Hmm, I'm not convinced. Why not assert dirty_check(user_data, { 'id': IsPositiveInt, 'avatar_file': IsStr(regex=r'/[a-z0-9\-]{10}/example\.png'), It would work just as well without abusing the == operator. Doing so seems like a bit of a gimmick (although the actual functionality of the library looks useful). Edit: Ah, I guess the difference is that dict.__eq__ (and list.__eq__ and so on) recursively tests equality of all child elements. So to support arbitrary nesting I think it really does have to be the equals operator.

scolvin 5y ago
I disagree, this is much less clear. It also don't work well with pytest's error output.
- scolvin 5y ago
  And it would be much more complex to implement, particularly with recursively nested types.

high_byte 5y ago

this is pretty neat!