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that approach gives me headaches to think about. Why not just have polymorphic functions? fn subset(superset, start, end){ // superset is type infe

that approach gives me headaches to think about. Why not just have polymorphic functions? fn subset(superset, start, end){ // superset is type inferred as long as it supports the [] operator // logic to collect superset[start] to superset[end] into an array and return it } with uniform function call syntax: [1,2,3,4,5,6].subset(1,4) == [2,3,4,5] If you really want to reuse a subset range, you can use lambdas/closures, or in this case a simple wrapper // in some code fn subset1to4(superset){ return subset(superset,1,4) } array.subset1to4() anotherArray.subset1to4()

nauticacom 5y ago
Sure, that works for some specific problems where you're computing a value from a defined set of data types. "Subset of this data" was an example I've encountered in the past and used here because it has clearly distinct cases—give me the whole thing, give me some index-delimited range, possibly others—but there are plenty of other examples that don't fit a polymorphic function model (and let's forget that I've never even used a language with polymorphic functions). As another example I've encountered in the past, let's say you have some object that can dynamically define fields. Once you define a field, you can retrieve its value or maybe some default value e.g. model = Model.new model.define("points", default: 1) model.store("points", 10) points = model.retrieve("points") puts points # => 10 Let's say doing anything with an undefined field is invalid. Here's my first pass at an implementation: class Model def initialize @fields = {} end def define(name, default: nil) @fields[name] = Field.new(name, default) end def retrieve(name) @fields[name].value end def store(name, value) @fields[name].value = value end end class Field attr_reader :name attr_accessor :value def initialize(name, value) @name = name @value = value end end Works great! One day a requirement comes along that default values need to be lambdas, too, which are called every time the value is retrieved. How do we implement that? One way is to add a conditional to the Field class: class Field attr_reader :name attr_writer :value def initialize(name, value) @name = name @value = value end def value if value.is_a?(Proc) @value.call else @value end end end But now Field knows that it can be passed a lambda, so testing it needs to account for that case (among many other considerations, probably, in a real-world system). And any time we add more cases for default values, let alone changes to regular values like type casting or something, the Field class becomes more complicated. I'd probably reach for a new object instead: class Model def initialize @fields = {} end def define(name, default: nil) @fields[name] = Field.new(name, nil, Default.for(default)) end def retrieve(name) @fields[name].value end def store(name, value) @fields[name].value = value end end class Field def initialize(name, value, default) @name = name @value = value @default = default end def value if @value.nil? @default.value else @value end end end class Default def self.for(indicator) if indicator.is_a?(Proc) Default::Dynamic.new(indicator) elsif indicator.nil? Default::None.new else Default::Static.new(indicator) end end class Static < Default def initialize(value) @value = value end def value @value end end class Dynamic < Default def initialize(callable) @callable = callable end def value @callable.call end end class None < Default def value nil end end end Now we've changed the conditional in the Field class to one that's actually relevant to it (do I have a value yet?) and won't change when the kinds of default values that it can accept change. Because we dependency-injected the Default object into the Field object, testing that conditional becomes a binary of retrieving the default value when no value is set, and retrieving the value once it's set. We can then test each kind of Default on its own, and changes to Default don't impact Field. If we really, really wanted to we could even eliminate the conditional in Field alltogether by unifying the interface for @default and @value such that they're both objects with a #value method (or maybe rename it to something else so we don't write @value.value). In either case we've made each piece simpler to reason about and pushed conditionals up the call stack so the resulting code is more straightforward. I can probably recall more examples of simplifications like this, but this is where I find inheritance the most useful: a known set of things that each polymorphically conform to some interface. In these examples I don't actually use the superclass for any shared behavior, but you can imagine a case where I might. One other benefit that I really like from the inheritance-object-modeling-as-pushing-up-conditionals perspective is that it makes you define what the different cases of something are as distinct objects, and give names to them. It's a similar benefit that falls out of using named sum types instead of signal values or tagged unions or something, but has the opposite effect (overall reduction of conditionals rather than proliferation).

nauticacom 5y ago

Sure, that works for some specific problems where you're computing a value from a defined set of data types. "Subset of this data" was an example I've encountered in the past and used here because it has clearly distinct cases—give me the whole thing, give me some index-delimited range, possibly others—but there are plenty of other examples that don't fit a polymorphic function model (and let's forget that I've never even used a language with polymorphic functions). As another example I've encountered in the past, let's say you have some object that can dynamically define fields. Once you define a field, you can retrieve its value or maybe some default value e.g. model = Model.new model.define("points", default: 1) model.store("points", 10) points = model.retrieve("points") puts points # => 10 Let's say doing anything with an undefined field is invalid. Here's my first pass at an implementation: class Model def initialize @fields = {} end def define(name, default: nil) @fields[name] = Field.new(name, default) end def retrieve(name) @fields[name].value end def store(name, value) @fields[name].value = value end end class Field attr_reader :name attr_accessor :value def initialize(name, value) @name = name @value = value end end Works great! One day a requirement comes along that default values need to be lambdas, too, which are called every time the value is retrieved. How do we implement that? One way is to add a conditional to the Field class: class Field attr_reader :name attr_writer :value def initialize(name, value) @name = name @value = value end def value if value.is_a?(Proc) @value.call else @value end end end But now Field knows that it can be passed a lambda, so testing it needs to account for that case (among many other considerations, probably, in a real-world system). And any time we add more cases for default values, let alone changes to regular values like type casting or something, the Field class becomes more complicated. I'd probably reach for a new object instead: class Model def initialize @fields = {} end def define(name, default: nil) @fields[name] = Field.new(name, nil, Default.for(default)) end def retrieve(name) @fields[name].value end def store(name, value) @fields[name].value = value end end class Field def initialize(name, value, default) @name = name @value = value @default = default end def value if @value.nil? @default.value else @value end end end class Default def self.for(indicator) if indicator.is_a?(Proc) Default::Dynamic.new(indicator) elsif indicator.nil? Default::None.new else Default::Static.new(indicator) end end class Static < Default def initialize(value) @value = value end def value @value end end class Dynamic < Default def initialize(callable) @callable = callable end def value @callable.call end end class None < Default def value nil end end end Now we've changed the conditional in the Field class to one that's actually relevant to it (do I have a value yet?) and won't change when the kinds of default values that it can accept change. Because we dependency-injected the Default object into the Field object, testing that conditional becomes a binary of retrieving the default value when no value is set, and retrieving the value once it's set. We can then test each kind of Default on its own, and changes to Default don't impact Field. If we really, really wanted to we could even eliminate the conditional in Field alltogether by unifying the interface for @default and @value such that they're both objects with a #value method (or maybe rename it to something else so we don't write @value.value). In either case we've made each piece simpler to reason about and pushed conditionals up the call stack so the resulting code is more straightforward. I can probably recall more examples of simplifications like this, but this is where I find inheritance the most useful: a known set of things that each polymorphically conform to some interface. In these examples I don't actually use the superclass for any shared behavior, but you can imagine a case where I might. One other benefit that I really like from the inheritance-object-modeling-as-pushing-up-conditionals perspective is that it makes you define what the different cases of something are as distinct objects, and give names to them. It's a similar benefit that falls out of using named sum types instead of signal values or tagged unions or something, but has the opposite effect (overall reduction of conditionals rather than proliferation).