BoundariesBoundaries

Dan Sugalskidan@sidhe.org

November 8, 2003

What the heck am I talking about?

BoundaryBoundary

Pronunciation: 'baun-d(&-)rEFunction: nounInflected Form(s): plural -ariesDate: 1626: something (as a line,

point, or plane) that indicates or fixes a limit or extent

Boundaries are everywhereBoundaries are everywhere

• Functions• Source Modules• CPU modes• Programs• Languages• People• Concepts

Boundaries provideBoundaries provide

• Categorization• Isolation• Inflection points• Constraint• Safety• Domain separation

Boundaries provideBoundaries provide

Perspective

Boundaries provideBoundaries provide

• Restriction• Inefficiency• Annoyance• Vicious classification

BoundariesBoundaries

• Used properly, they provide structure and framework

• Used improperly, they’ll strangle the life out of a project

• Which is which is always up for argument

In shortIn short

A power so great it can only be used for

good or evil!

Reality CheckReality Check

• The problem’s just too big to fit in your brain all at once

• Unless it’s a very small problem• Or a scary-sized brain

The landscape isn’t mobileThe landscape isn’t mobile

• “Problem points” are linked• They can be moved (some)• They exist whether you want to

consider them or not

Division of LaborDivision of Labor

• Who does what• Who doesn’t do what• Who provides what to whom• Who has to understand what

API segregationAPI segregation

• What you have to know to use a library

• What data belongs to whom• How to cross the boundary• For code, defines part of the

boundary

ParadigmsParadigms

• Different languages act differently• Drawing boundaries keeps things

separate• Beats having to think in Forth, C,

Scheme, Prolog, APL, and Smalltalk simultaneously

Poor definition can be harmful

Poor definition can be harmful

• Sloppy APIs• Limits on forward changes• Confusion amongst users• Confusion amongst developers• Force extra work

Use them to your advantageUse them to your advantage

• Partition problem spaces to fit your brain

• …And other people’s brains• Install inflection points• Provide guarantees• Hide cheating

Just RememberJust Remember

Always, always, place them on purpose

One More ThingOne More Thing

Ignore the landscape at your peril