Message chain smell
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Revision as of 07:29, 1 August 2009
The message chain smell arises when a particular class is highly coupled to other classes in chain-like delegations. To illustrate this smell, suppose we have Class A who needs data from Class E. To retrieve this data, object A firstly needs to retrieve object E from object D from object C from object B. Thus we have something like this:
a.getB().getC().getD().getE().getTheData();
The problem which lies here is that as A tried to access the data at Class E, A becomes unnecessarily coupled to class B, C, D along the way; when it needs only to get the data from E.
However, sometimes delegations are needed, and thus delegation chains with a couple of links are often considered to be harmless. The argument as to how many links a chain can reasonably have is often related to other factors. Consider the other design maxims mentioned below for more guidance related to designs with highly coupled chained delegations.
Refactoring Techniques
- Hide Delegate in conjunction with Extract Method or Move methods - to minimise some of the chaining.
- Consider Law of Demeter or Tell, don't ask design maxims.
