{"id":1324,"date":"2010-07-24T00:58:30","date_gmt":"2010-07-23T14:58:30","guid":{"rendered":"http:\/\/www.somethinkodd.com\/oddthinking\/?p=1324"},"modified":"2010-07-27T17:17:30","modified_gmt":"2010-07-27T07:17:30","slug":"enumerating-features-of-enumerated-types","status":"publish","type":"post","link":"https:\/\/www.somethinkodd.com\/oddthinking\/2010\/07\/24\/enumerating-features-of-enumerated-types\/","title":{"rendered":"Enumerating Features of Enumerated Types"},"content":{"rendered":"

If you aren’t into programming language design, you can skip this.<\/p>\n

For the rest of us, I want to talk enumerated types. It is a discussion I have with myself frequently.<\/p>\n

Simple Modelling Challenge<\/h3>\n

Consider how you would model this decision at your local chip shop, in your favourite programming language.<\/p>\n

Milkshakes can be chocolate, vanilla or strawberry – that’s all they sell. They can be small, medium or large.<\/p>\n

How to Assess The Result?<\/h3>\n

Here are some questions for you:<\/p>\n

Does your language ensure that the milkshake could only be those flavours. Will it permit someone to say a milkshake is blueberry flavoured?<\/p>\n

Does your language support the concept that large is greater than medium? (Conversely, can you say that Vanilla and Strawberry do not support the greater-than relationship?)<\/p>\n

Can you loop over the flavours?<\/p>\n

Do you have to specify an internal integer representation? Or will your language assign values for you?<\/p>\n

Can you learn that internal integer representation for use as a key? What about for use as serialisation (which requires you to be able to go the other way, too, from integer to enumerated value)?<\/p>\n

Can you override the internal integer representation? e.g. to map large to its size in millilitres.<\/p>\n

If you want to argue that I just overstepped the meaning of an enumerated type, I will agree with you. However, it often comes up during development.<\/div>\n

Is there a text representation available so you can easily print “Strawberry” rather than 2?<\/p>\n

Some I Prepared Earlier<\/h3>\n

Here are what I believe the answers are for several classic languages – some have more than one way to implement this. [Source: Memory and Wikipedia<\/a>]<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Language (Technique)<\/th>\nType-Checked<\/th>\nOrder Available?<\/th>\nOrder Mandatory?<\/th>\nIterable?<\/th>\nVisible integer representation?<\/th>\nSerialisable?<\/th>\nHas Auto-Inc value<\/th>\nHas Overridable value<\/th>\nHas Text Representation<\/th>\n<\/tr>\n
Pascal<\/th>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nFALSE3<\/sup><\/td>\nTRUE<\/td>\nFALSE<\/td>\nFALSE<\/td>\n<\/tr>\n
C (Enum)<\/th>\nFALSE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nFALSE<\/td>\nTRUE<\/td>\nFALSE6<\/sup><\/td>\nTRUE<\/td>\nTRUE<\/td>\nFALSE<\/td>\n<\/tr>\n
C++ (Enum)<\/th>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nFALSE<\/td>\nTRUE<\/td>\nFALSE6<\/sup><\/td>\nTRUE<\/td>\nTRUE<\/td>\nFALSE<\/td>\n<\/tr>\n
C\/C++ (Const)<\/th>\nFALSE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nFALSE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nFALSE<\/td>\nTRUE<\/td>\nFALSE<\/td>\n<\/tr>\n
Java<\/th>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\n<\/tr>\n
Python (Dict)<\/th>\nManual2<\/sup><\/td>\nTRUE5<\/sup><\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nFALSE4<\/sup><\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\n<\/tr>\n
Python (Set)<\/th>\nManual2<\/sup><\/td>\nFALSE<\/td>\nN\/A<\/td>\nTRUE<\/td>\nFALSE<\/td>\nFALSE4<\/sup><\/td>\nN\/A<\/td>\nFALSE<\/td>\nTRUE<\/td>\n<\/tr>\n
Python (Enum Class1<\/sup>)<\/th>\nManual2<\/sup><\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE?<\/td>\nTRUE<\/td>\nFALSE4<\/sup><\/td>\nFALSE<\/td>\nTRUE<\/td>\nFALSE<\/td>\n<\/tr>\n
SQL<\/th>\nTRUE?<\/td>\nTRUE<\/td>\nTRUE<\/td>\nFALSE?<\/td>\nTRUE?<\/td>\nTRUE<\/td>\nTRUE<\/td>\nFALSE<\/td>\nTRUE?<\/td>\n<\/tr>\n
Ada<\/th>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\n<\/tr>\n
C#<\/th>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\nTRUE<\/td>\n<\/tr>\n<\/table>\n

1<\/sup> I frequently use this Enum class<\/a> I found on the web. I frequently regret it, because I keep forgetting it doesn’t offer everything Ada did (in 1983!).<\/p>\n

2<\/sup> Python is dynamically typed. You can write, for example, assert flavour in milkshake_flavours<\/code>, but it won’t be checked for you, so you need to do it explicitly.<\/p>\n

3<\/sup> Standard Pascal doesn’t support it but several implementations, and derived languages, do.<\/p>\n

4<\/sup> It is possible to create back-mappings, but they are look-ups, not trivial type-coercions.<\/p>\n

5<\/sup> By comparing the values from the dictionary yourself: CUP_SIZE['large'] > CUP_SIZE['small']<\/code> Without manual sorting, iteration will not be in this order.<\/p>\n

6<\/sup> De-serialising a value known to be good can be done for free – a coercion in C, or a cast in C++. Detecting whether such a value is good is hard.<\/p>\n

Conclusion<\/h3>\n

Sometimes, I miss Ada.<\/p>\n

[Updated to include C#, separate C++ enums and indicate Java’s overridable nature, iterability and text representation, according to help from commenters. Thank you.]<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"

In which Enumerated Types are compared by programming language<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_s2mail":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-1324","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/www.somethinkodd.com\/oddthinking\/wp-json\/wp\/v2\/posts\/1324","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.somethinkodd.com\/oddthinking\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.somethinkodd.com\/oddthinking\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.somethinkodd.com\/oddthinking\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.somethinkodd.com\/oddthinking\/wp-json\/wp\/v2\/comments?post=1324"}],"version-history":[{"count":20,"href":"https:\/\/www.somethinkodd.com\/oddthinking\/wp-json\/wp\/v2\/posts\/1324\/revisions"}],"predecessor-version":[{"id":1349,"href":"https:\/\/www.somethinkodd.com\/oddthinking\/wp-json\/wp\/v2\/posts\/1324\/revisions\/1349"}],"wp:attachment":[{"href":"https:\/\/www.somethinkodd.com\/oddthinking\/wp-json\/wp\/v2\/media?parent=1324"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.somethinkodd.com\/oddthinking\/wp-json\/wp\/v2\/categories?post=1324"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.somethinkodd.com\/oddthinking\/wp-json\/wp\/v2\/tags?post=1324"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}