pragmatic-programmer

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The Pragmatic Programmer Framework

A systems-level approach to software craftsmanship from Hunt & Thomas' "The Pragmatic Programmer" (20th Anniversary Edition). Apply these meta-principles when designing systems, reviewing architecture, writing code, or advising on engineering culture -- how to think about software, not just how to write it.

Core Principle

Care about your craft. Software development demands continuous learning, disciplined practice, and personal responsibility -- pragmatic programmers think beyond the immediate problem to context, trade-offs, and long-term consequences. Great software comes from great habits: avoid duplication ruthlessly, keep components orthogonal, and treat every line of code as a living asset that must earn its place. The goal is not perfection -- it is systems that are easy to change, easy to understand, and easy to trust.

Scoring

Goal: 10/10. Score against the seven Quick Diagnostic rows: award ~1.4 points per row answered "yes" (7 yes = 10). Then band the result:

• 9-10: every principle holds -- DRY knowledge, orthogonal layers, a working tracer slice, contracts at boundaries, no broken windows, reversible vendor/DB choices, ranged estimates.
• 5-6: 1-2 violations that cost real change-effort (e.g. business logic coupled to the DB, single-point estimates).
• <=3: pervasive duplication, global state, or accumulated broken windows -- entropy is winning.

Always state the score, name the failing diagnostic rows, and give the specific fix from the Action column to reach 10/10.

The Seven Meta-Principles

Seven principles for building software that lasts:

1. DRY (Don't Repeat Yourself)

Core concept: Every piece of knowledge must have a single, unambiguous, authoritative representation within a system. DRY is about knowledge, not code -- duplicated logic, business rules, or configuration are far more dangerous than duplicated syntax.

Why it works: Duplicated knowledge must be changed in multiple places; eventually one gets missed, introducing inconsistency. DRY reduces the surface area for bugs and makes systems easier to change.

Key insights:

• DRY applies to knowledge and intent, not textual similarity -- two identical code blocks serving different business rules are NOT duplication
• Four types of duplication: imposed (environment forces it), inadvertent (developers don't realize), impatient (too lazy to abstract), inter-developer (multiple people duplicate)
• Comments that restate the code violate DRY -- explain why, not what
• Database schemas, API specs, and documentation duplicate knowledge unless generated from a single source
• The opposite of DRY is WET: "Write Everything Twice" or "We Enjoy Typing"

Code applications:

See: references/dry-orthogonality.md when classifying a specific duplication or deciding whether two code blocks are truly the same knowledge -- per-type examples and mitigations for the four duplication types.

2. Orthogonality

Core concept: Two components are orthogonal if changes in one do not affect the other. Design systems where components are self-contained, independent, and have a single, well-defined purpose.

Why it works: Decoupling localizes change -- a fix in one module can't ripple into unrelated ones, so blast radius stays bounded. Change the database layer and the UI should not break; change the auth provider and business logic should not care.

Key insights:

• Ask: "If I dramatically change the requirements behind a function, how many modules are affected?" The answer should be one
• Eliminate effects between unrelated things -- a logging change should never break billing
• Layered architectures promote orthogonality: presentation, domain logic, data access
• Avoid global data -- every consumer of global state is coupled to it
• Frameworks that force you to inherit from their classes reduce orthogonality

Code applications:

See: references/dry-orthogonality.md when measuring coupling or refactoring toward decoupled layers -- the change-impact and stranger tests, layered-architecture diagram, and the helicopter analogy.

3. Tracer Bullets and Prototypes

Core concept: Tracer bullets are end-to-end implementations connecting all layers of the system with minimal functionality. Unlike prototypes (which are throwaway), tracer bullet code is production code -- thin but real.

Why it works: Tracer bullets give immediate end-to-end feedback before you invest in filling out every feature. Users see something real, developers have a framework to build on, and integration issues surface early.

Key insights:

• Tracer bullet: thin but complete path through the system (UI -> API -> DB) -- you keep it
• Prototype: focused exploration of a single risky aspect -- you throw it away
• Use tracer bullets when "shooting in the dark" -- vague requirements, unproven architecture
• If a tracer misses, adjust and fire again -- the cost of iteration is low
• Label prototypes clearly as throwaway -- never let one become production code

Code applications:

See: references/tracer-bullets.md when deciding tracer vs. prototype on a new project or building a walking skeleton -- the shooting-in-the-dark decision, iteration loop, and common pitfalls.

4. Design by Contract and Assertive Programming

Core concept: Define and enforce the rights and responsibilities of software modules through preconditions (what must be true before), postconditions (what is guaranteed after), and invariants (what is always true). When a contract is violated, fail immediately and loudly.

Why it works: Contracts make assumptions explicit. Instead of silently corrupting data or limping along in an invalid state, the system crashes at the point of the problem -- dead programs tell no lies.

Key insights:

• Preconditions: caller's responsibility -- "I accept only positive integers"
• Postconditions: routine's guarantee -- "I will return a sorted list"
• Invariants: always true -- "Account balance never goes negative"
• Crash early: a dead program does far less damage than a crippled one
• Use assertions for things that should never happen; error handling for things that might
• In dynamic languages, implement contracts through runtime checks and guard clauses

Code applications:

See: references/contracts-assertions.md when adding contracts to a routine or deciding assertion vs. error handling -- worked pre/post/invariant patterns, dynamic-language guard clauses, and the assertions-vs-error-handling boundary.

5. The Broken Window Theory

Core concept: One broken window -- a badly designed piece of code, a poor management decision, a hack that "we'll fix later" -- starts the rot. Once a system shows neglect, entropy accelerates and discipline collapses.

Why it works: Psychology. When code is clean, developers feel social pressure to keep it that way; when code is already messy, the threshold for adding more mess drops to zero. Quality is a team habit, not an individual heroic effort.

Key insights:

• Don't leave broken windows (bad designs, wrong decisions, poor code) unrepaired
• If you can't fix it now, board it up: a TODO with a ticket, a disabled feature, a stub
• Be a catalyst for change: show people a working glimpse of the future (stone soup)
• Watch for slow degradation (boiled frog) -- monitor tech debt metrics over time
• The first hack is the most expensive because it gives permission for all subsequent hacks

Code applications:

See: references/broken-windows.md when a team is normalizing neglect or you need to drive a turnaround -- repair strategies, the stone-soup catalyst play, and building a culture of quality.

6. Reversibility and Flexibility

Core concept: There are no final decisions. Build systems that make it easy to change your mind about databases, frameworks, vendors, architecture, and deployment targets -- the cost of change should be proportional to the scope of change.

Why it works: Requirements change, vendors get acquired, technologies fall out of favor. If your architecture hard-codes assumptions about any of these, every change becomes a rewrite; flexible architecture treats decisions as configuration, not structure.

Key insights:

• Abstract third-party dependencies behind your own interfaces -- never let vendor APIs leak into business logic
• The "forking road" test: could you switch from Postgres to DynamoDB in a week? If not, you're coupled
• Metadata-driven systems (config files, feature flags) are more flexible than hard-coded logic
• YAGNI applies to premature abstraction too -- don't build flexibility you don't need yet
• Reversibility is not predicting the future; it's not painting yourself into a corner

Code applications:

See: references/reversibility.md when committing to a vendor or framework, or weighing how reversible a decision must be -- per-layer reversibility patterns, the forking-road test, and when NOT to optimize for reversibility.

7. Estimation and Knowledge Portfolio

Core concept: Learn to estimate reliably by understanding scope, building models, decomposing into components, and assigning ranges. Manage your learning like a financial portfolio: invest regularly, diversify, and rebalance.

Why it works: Honest estimation builds trust with stakeholders ("1-3 weeks" beats a confidently wrong "2 weeks"). A knowledge portfolio keeps you relevant as technologies shift -- the programmer who stops learning stops being effective.

Key insights:

• Ask "what is this estimate for?" -- context determines precision (budget planning vs. sprint planning)
• Use PERT: (Optimistic + 4x Most Likely + Pessimistic) / 6
• Decompose into components and estimate each; the sum is more accurate than a single guess
• Keep an estimation log: compare estimates to actuals and calibrate
• Portfolio rules: invest regularly (learn weekly), diversify beyond your stack, mix safe and speculative bets, learn emerging tech early (buy low)

Code applications:

See: references/estimation-portfolio.md when producing an estimate you'll be held to or calibrating past misses -- the PERT and decomposition procedures, an estimation-log calibration loop, and portfolio rebalancing.

Common Mistakes

Quick Diagnostic

Further Reading

• The Pragmatic Programmer: Your Journey to Mastery, 20th Anniversary Edition by Andrew Hunt and David Thomas

About the Authors

Andrew Hunt and David Thomas co-founded the Pragmatic Bookshelf and were among the 17 original authors of the Agile Manifesto. Thomas coined "DRY" and "Code Kata" and co-authored Programming Ruby (the Pickaxe book); Hunt focuses on how teams learn, communicate, and maintain quality. Together they wrote The Pragmatic Programmer, one of the most influential software books ever published.