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Table of Contents
Uniformity Principle (UP)
Variants and Alternative Names
Context
Principle Statement
Solve similar problems the same way.
Description
Rationale
Strategies
- Use the same naming scheme everywhere
- Use the same techniques and mechanisms everywhere
- In similar methods use the same order of parameters
Caveats
See section contrary principles.
Origin
Evidence
Relations to Other Principles
Generalizations
- Murphy's Law (ML): A typical source of mistakes are differences. If similar things work similarly, they are more understandable. But if there are subtle differences in how things work, it is likely that someone will make the mistake to mix this up.
Specializations
Contrary Principles
Note that UP can be contrary to virtually every other principle as it demands neglecting other principles in favor of uniformity.
- Keep It Simple Stupid (KISS): Sometimes UP demands more complex solutions because they are already applied elsewhere and for the sake of uniformity shall also be applied in simpler contexts where they would not be necessary.
- Model Principle (MP): UP may demand adhering to a certain naming scheme, which may not be best with respect to MP. See example 1: naming schemes.
Complementary Principles
- Principle of Least Surprise (PLS): When applying UP, PLS should also be considered for naming modules. See example 1: naming schemes.
Principle Collections
Examples
Example 1: Naming Schemes
A typical example of the application of UP is the naming of method identifiers for common container classes like stacks or queues. This also shows that there are several ways to apply this principle.
Stacks typically have the methods push
, pop
and peek
(sometimes also called top
). push
puts an item onto the stack, pop
removes the top most item and peek
retrieves the value of the top most item without removing it from the stack. This is how the common stack model describes this data structure (see MP). Applying UP to this naming decision means that the methods should be named precisely as they are named everywhere else also. So a developer knowing the model or other implementations of the model will immediately know how to use this module as well. In this case MP and UP demand the same thing. PLS is satisfied here as well as a developer knowing stacks will expect exactly that.
Queues on the other hand typically have the methods enqueue
, dequeue
, and peek
(or front
/first
or the like). MP would demand naming the operations of a Queue
module exactly that way. But there are several ways Up can be applied here. The one way is to apply the principle just like above. Resulting in methods enqueue
and dequeue
. This is how it is done in .NET1). The other way is to consider the method identifiers of the Stack
module. A possible application of UP could be to demand naming the queue methods just like the stack methods, meaning also push
, pop
and peek
. This is the naming scheme which was chosen in the Delphi RTL2). Here MP and UP are contrary. A further downside of this approach is that pop
and push
methods might be surprising for a queue class. So PLS would oppose this solution.
A third possibility is to find a common abstraction and to apply a very general naming scheme to all descendant classes (stack classes, queue classes and others). This is the way it is done in Eiffel3). Here there the method names are put
, remove
and item
regardless of the concrete data structure. This is contrary to MP but creates a uniform naming scheme throughout the API. So there is less uniformity across APIs but stronger uniformity within the API. MP and UP are here contrary too. For PLS this means that a developer who is used to this philosophy is never surprised by having these methods. But developers new to it might be nevertheless.