D esign S mells The 7 Odors of R otting S oftware G iorgio V espucci – S oftware F actory R oma

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W hat is

S oftware D esign

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“ […] the design of a software project is documented primarily by its source code .” Robert C. Martin

The source code is the design.

Abandoned code rots .

When it rots, it smells .

7 S mells

1. R igidity

The tendency for software to be difficult to change , even in simple ways. The design is hard to change .

2. F ragility

The tendency of a program to break in many places when a single change is made. The design is easy to break .

3. I mmobility

It is hard to disentangle the system into components that can be reused in other systems. The design is hard to reuse .

4. V iscosity

S oftware viscosity

Design -preserving methods vs. Hacks

E nvironment viscosity

Slow and inefficient development environment Very long compile times Hours to check-in Several minutes to deploy

Doing things wrong is easier than doing things right .

5. N eedless C omplexity

Elements not currently useful in the design. O verdesign.

6. N eedless R epetition

C ut- a nd- p aste is useful for text-editing, but can be disastrous for c ode- e diting.

The design contains repeating structures that could be unified under a single abstraction.

7. O pacity

The tendency of a module to be difficult to understand .

Code written in a clear and expressive manner vs. Code written in an opaque and convoluted manner.

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W hat is a

D esign S mell

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A d esign s mell is a symptom .

It’s a violation of P rinciples.

S . O . L . I . D . Principles

T o be c ontinued...