On Thu, Oct 12, 2017 at 9:20 AM, Mike Miller <python-...@mgmiller.net> wrote:
> > On 2017-10-12 00:36, Stéfane Fermigier wrote: > >> "An object that is not defined by its attributes, but rather by a thread >> of continuity and its identity." (from https://en.wikipedia.org/wiki/ >> Domain-driven_design#Building_blocks) >> > > Not sure I follow all this, but Python objects do have identities once > instantiated. e.g. >>> id('') > > It seems to me that the quoted document is attempting to make a distinction similar to the one between classes (entities) and instances (value objects). The reason I liked "row" as a name is because it resembles "vector" and hence is loosely assocaited with the concept of a tuple as well as being familiar to database users. In fact the answer to a relational query was, I believe, originally formally defined as a set of tuples. Sometimes one can simply be too hifalutin' [ http://www.dictionary.com/browse/hifalutin], and language that attempts to be precise obscures meaning to the less specialised reader. See also the more general Wikipedia definition "An entity is something that >> exists as itself, as a subject or as an object, actually or potentially, >> concretely or abstractly, physically or not." ( >> https://en.wikipedia.org/wiki/Entity). >> >> In the context of DDD, entities are usually opposed to value objects: "An >> object that contains attributes but has no conceptual identity. They should >> be treated as immutable.". (https://en.wikipedia.org/wiki >> /Domain-driven_design#Building_blocks) >> >> Attrs, and by extension the dataclass proposal (I guess), provide some >> support for both: >> >> - Providing support for quickly constructing immutable objects from a bag >> of attributes, and providing equality based on those attributes, it helps >> implement Value Objects (not sure much more is needed actually) >> >> - By supporting equality based on some "primary key", it will also help >> with maintaining the concept of "equality" in entities. >> > > I don't believe either module particularly supports or restricts > immutability? > > -Mike > >
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