Is there a name for a dictionary that returns the key as the value by default? [closed]

Question

A dictionary that returns the key as the value by default can be used in cases where exceptions or translation is needed.

E.g. One could do

i18n = SpecialDict()

if spanish:
    i18n["Hello"] = "Hola"

print(i18n["Test"]) # prints Test
print(i18n["Hello"]) # prints Hola if spanish

I18n is just an example, there are other (probably better) uses.

Is there a name for this dictionary / pattern?

Edit

Wow, I did not expect such a backsplash. Just to make it clear, this type of dictionary is not "defective" or "broken". It is a simple and elegant solution for a specific type of problem, and I have used this pattern with great success in my career. If you fail to see a usage for this then please move along to another question.

As for gnat's comment, I was not aware that questions like this are not welcome here. I'm sorry for that. I would delete my question but there is already an answer (which actually does not answer my question at all) so I'll just flag it for closure.

Edit 2

Since I have not found a name or usage of this, and this (sadly short-lived) question did not bring up anything either I hereby name this pattern

Data Aspect

and the dictionary-like object a

Data Aspect Map

I would love to post an answer to this question with a more detailed definition, description and maybe some examples and welcome feedback to this pattern, but I can't, since this question is on hold.

Answer 1

For the use case you've described, I think it's a valid pattern. However, there is no name for this, AFAIK.

In Java 8, there is a Map.getOrDefault method, which almost does that:

String greetingKey = "Hello";

Map<String, String> i18n = new HashMap<>();
i18n.put(greetingKey, "Hola");

String greeting = i18n.getOrDefault(greetingKey, greetingKey);

Just using a key as default value - a bit more verbose than your version, if it was implemented as a class with overridden get method.

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There is more general pattern to that: "if there is no value for a requested key, return result of some function applied to a key (and other data in a map/dictionary)" - in your case it's just an identity function applied to a key. Same pattern can be used for interpolation, for example.

It may be called "interpolated map", where in your case interpolation is degenerated to just use a key (argument) and no "neighbor points" (compare: linear interpolation uses two neighbors). Yet, I've never heard of such a thing being an object-oriented pattern. It is more of a functional design pattern, which just uses higher-order functions, hence no specific name needed.

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EDIT: Your approach can be considered as flawed because there is an implicit contract on map/dictionary, which states: "if containsKey returns false, then get must return null" (opposite may not hold if null is a valid value).

There probably is some code which relies on this contract, and your implementation breaks it, hence it may cause runtime errors.

Answer 2

This doesn't sound like any Dictionary class I've heard of, but it could be trivially implemented by wrapping a dictionary in another class (or inheriting from it) and modifying the Get behavior.