Foundation Runtime Classpath

Class Loading

Klyn resolves classes through a deterministic search order. The rule is deliberately strict: standard library classes are always resolved before application classes, so local files cannot impersonate or shadow core klyn.* types.

Search Order

When the runtime looks for a class source file, it checks these roots in order:

  1. $KLYN_HOME/lib, the standard library root.
  2. The directory containing the startup .kn file passed to klyn.
  3. Each directory passed through -kp or --klasspath, from left to right.
  4. Each directory listed in $KLASSPATH, from left to right.
  5. The current working directory, if it was not already added as the startup directory.
Security first

This order prevents an application or launch directory from replacing standard library classes. For example, a local klyn/String.kn will not override the real klyn.String implementation.

Startup Source Directory

The startup directory is the folder that contains the script you launch, not necessarily the shell current directory. 

cd ~/Klyn
klyn samples/gui/ClockSample.kn

In this example, Klyn searches ~/Klyn/samples/gui before explicit klasspath roots, before $KLASSPATH and before ~/Klyn. This keeps applications relocatable without making the current directory more powerful than the application root.

Package Layout

Klasspath entries are source roots. A type declared in package my.app.core must therefore be stored below my/app/core within one of those roots. Klyn validates this correspondence and rejects a mismatched declaration. A source without a package declaration remains in the default package regardless of its physical directory.

Using Klasspath Roots

Use -kp or --klasspath when an application depends on additional source roots outside its startup directory. On Linux, entries are separated with :. On Windows, entries are separated with ;. 

klyn -kp "/opt/klyn-libs:/home/me/shared-klyn" app/Main.kn
klyn --klasspath "/opt/klyn-libs" app/Main.kn

For reproducible launch commands, prefer the explicit command-line option. Environment variables remain useful for developer shells and CI jobs that share a common dependency layout. 

export KLASSPATH="/opt/klyn-libs:/home/me/shared-klyn"
klyn app/Main.kn

Klyn also accepts the historical KLYNPATH variable when KLASSPATH is not defined, but new projects should use KLASSPATH.

Compilation Cache

Class lookup and object caching are separate concerns. Once a source file has been resolved, the compiler reuses its cached .o file when that object is newer than the corresponding .kn source. If the source changes, Klyn recompiles it automatically.

Next Step

Continue with Coding Conventions before moving to the core syntax chapters.