David Bernstein

Software developer and author of Beyond Legacy Code ( and Prompt Engineering for Everyone (

[David Bernstein @ToBeAgile]

The forces changed.

That’s often the signal that a design needs to evolve.

New episode:
When One Pattern Isn’t Enough
https://t.co/rryQ3kbm77

We explore Template Method, Strategy, Abstract Factory, and why patterns naturally work together.

#DesignPatterns #SoftwareDesign

[David Bernstein @ToBeAgile]

Mediator doesn’t remove complexity.

It gives coordination a home.

New episode:
Why Your Code Feels Like a Mess (Mediator Pattern)

https://t.co/PRYVZPo87S

#DesignPatterns #SoftwareArchitecture #MediatorPattern

[David Bernstein @ToBeAgile]

Polling asks:

“Did something change yet?”

Observer says:

“I’ll tell you when it happens.”

That tiny shift changes the architecture completely.

New episode:
Why Polling Breaks Your Architecture (Observer Pattern)

https://t.co/dpMNjSeRcp

[David Bernstein @ToBeAgile]

New blog post: AI Is Revealing How We Think - https://t.co/786IgCqfc3

[David Bernstein @ToBeAgile]

“The same input means different things in different states.”

That’s the REAL insight behind the State Pattern.

Not “remove conditionals.”
Not “use polymorphism.”

Meaning itself changes with context.

New episode:
Why Your Code Breaks When State Changes
https://t.co/GPVgEtJwvK

[David Bernstein @ToBeAgile]

When actions become objects:
behavior gains identity.

And once behavior has identity:
systems can reason about behavior structurally.

That’s one of the deepest ideas in object-oriented design.

New video:
https://t.co/H7YHrZ2Bpg

[David Bernstein @ToBeAgile]

Patterns don’t solve problems.

They define how variation behaves.

If your design feels wrong…

it’s usually not the pattern.

It’s the variation.

New video
https://t.co/T0sR2l3zCb

[David Bernstein @ToBeAgile]

We’re not just creating objects.
We’re making decisions.
And when those decisions spread across your system…
things get out of control.
That’s where Factory comes from.
New video:
https://t.co/lnJTIskiE0

[David Bernstein @ToBeAgile]

New Blog Post: Why AI Exposes Our Weakest Design Skills - https://t.co/GiriNfHiv8

[David Bernstein @ToBeAgile]

If/else isn’t the problem.

Where the decision lives… is.

That’s the real reason Strategy Pattern exists.

Once you see it, you’ll stop overengineering—and start designing.

New video
https://t.co/Bm8CBEkuxm

[David Bernstein @ToBeAgile]

Happy Earth Day!

[David Bernstein @ToBeAgile]

Duplicate code isn’t the problem.

It’s the clue.

It’s your system trying to express a concept it doesn’t yet have.

Once you see that… design patterns stop being recipes and start being discoveries.

New video
https://t.co/3TqLR6QpPP

[David Bernstein @ToBeAgile]

Most developers memorize design patterns.

Senior developers see structure.

The difference?

They ask:
“What’s the same?”
“What’s different?”

Discover the key skill for working with design patterns, watch the video!
https://t.co/5FewSrua0Z

[David Bernstein @ToBeAgile]

Most developers see code as steps.
Experienced developers see structure.

New video:
https://t.co/fmj7o2Xpm7

Seeing Patterns in Problems

Directions tell you what to do.
Maps show you what exists.

That shift is the foundation of design patterns.

[David Bernstein @ToBeAgile]

New blog post: Design Signals: How to Spot Agency in Code - https://t.co/Q42oM3xk8U

[David Bernstein @ToBeAgile]

Tweet / X

Emergent design doesn’t mean “skip design.”

It means design safely while the system evolves.

But it only works if you can refactor without fear.

That requires tests.

New video about Emergent Design:

https://t.co/4St4rb3XD7

[David Bernstein @ToBeAgile]

Design patterns aren’t solutions.

They’re signals.

Signals that reveal the forces inside a problem.

If the force isn’t there → the pattern is wrong.

New video:
Patterns Aren’t Solutions (and Never Were)

https://t.co/qICoY73tE2

[David Bernstein @ToBeAgile]

Most developers think testability is about tests.

It’s actually about design.

When tests are painful → your design is telling you something.

New video:
Testability Is the Ultimate Code Smell Detector

https://t.co/MkqXNiJfpu

[David Bernstein @ToBeAgile]

Most rigid systems aren’t complex.

If construction and usage live in the same function, every new requirement edits that crossroads.

Factories centralize identity.

Create. Connect. Return.

New video: Where Should Decisions Live in Code?
https://t.co/Hl8869qE1v

[David Bernstein @ToBeAgile]

5 optional features.

32 subclasses.

That’s not bad design.

That’s math.

Variation belongs in data — not types.

New video: Class Explosion (and how to stop it)
https://t.co/Ezop09zIvA