majiayu000 General vs. Special-Purpose Review Lens
When invoked with $ARGUMENTS, focus the analysis on the specified file or module. Read the target code first, then apply the checks below.
General-purpose modules are surprisingly simpler, deeper and less effort to build. They produce better information hiding and can even provide these benefits when used in a single context. Because a general-purpose interface doesn't need to know about specific callers, the knowledge always stays where it belongs.
When to Apply
- Designing a new module, API, or utility
- When a module has use-case-specific logic embedded in it
- When a module's interface is cluttered with rarely-used parameters
- When deciding between a flexible API and a specific one
Core Principles
The Generality Test
"What is the simplest interface that will cover all my current needs?" — John Ousterhout, A Philosophy of Software Design
Not "the most general interface possible." The target is somewhat general-purpose.
- Functionality: Scoped to current needs. Doesn't build features you don't need.
- Interface: General enough to support multiple uses. Doesn't tie it only to today's caller.
A general-purpose interface is usually simpler than a special-purpose one. Fewer methods means lower cognitive load. Fewer methods per capability is the signal of increasing generality.
Two companion questions:
- In how many situations will this method be used? If exactly one, it's over-specialized.
- Is this API easy to use for my current needs? If callers must write loops or compose many calls for basic tasks, the abstraction level is wrong.
Special-General Mixture
Special-purpose code mixed into a general-purpose module makes it shallower. Two forms:
At the Interface
Methods or parameters that only serve specific callers. The interface widens, and policy decisions from a higher layer get encoded in a lower one.
Inside Method Bodies
Special cases tend to show up as extra if statements. Instead of adding more of them, try to create a design where they disappear. A search function that returns null when nothing is found forces every caller to check for null before using the result. If you return an empty list instead, the check loop runs zero times on its own with no extra check required.
Getters/Setters as Representation Leakage
Declaring a field private then providing getFoo/setFoo does not constitute information hiding. The variable's existence, type, and name are fully visible. Callers depend on the representation.
Before writing a getter or setter: should callers know about this property at all? A rename() method absorbs related logic and hides the representation. The goal is for the module to do work, not expose data.
Defaults as a Depth Tool
Every sensible default is one less decision pushed to callers. If nearly every user of a class needs a behavior, it belongs inside the class by default.
Gatekeeping question: "Will callers be able to determine a better value than we can determine here?" The answer is usually no.
The Default Position
When unsure, err on the side of slightly more general. A slightly-too-general interface has unused capabilities (low cost). A slightly-too-special interface requires a rewrite when the second use case arrives (high cost).
But "slightly more general" means one step, not three. Generality should come from simplifying the interface, not from adding parameters.
Review Process
- Identify the general mechanism: What is the core operation?
- Separate special from general: Is caller-specific logic in the core? Special-case
ifbranches that could be eliminated? - Apply the generality test: Simplest interface that covers all current needs?
- Audit getters/setters: Exposing representation or abstraction?
- Review defaults: Could required parameters become optional?
- Recommend: Push specialization to edges. Deepen with defaults.
Red flag signals for generality are cataloged in red-flags (Special-General Mixture, Overexposure).