22.5. Context

The context or environment from which a script is executed can make a huge difference to its speed. This is in large measure because Apple events are expensive. In particular, what makes them expensive is the context switch involved in communicating between one application and another. Thus it is typically fastest, where possible, to run a script from within the application it targets. If an application has a Script menu, therefore, it is worth putting the script there and executing it from there to see if this makes it faster.

(But also, there are some contexts that are inherently slower than others, for no discernable reason; it has something to do with how these contexts are programmed and that's that.)

Here's a test script:

set x to (get current date)
repeat 500 times
    tell application "iTunes"
        get name of it
    end tell
end repeat
set y to (get current date)
set z to (y - x)
tell application "Finder"
    activate
    display dialog z
end tell

Table 22-1 shows some rough timings on my machine for running that script from within various contexts.

Table 22-1. Timings for the same script executed in different contexts

Context	Timing
iTunes's Script Menu	0.15 second
Red Sweater FastScripts	0.5 second
Script Debugger	1.5 seconds
Apple's Script Menu	8 seconds
Script Editor	9 seconds
DragThing	Timed out after 500 seconds

Many external factors affect speed , so no absolute lessons can be drawn from a simple, unscientific test such as this; but clearly it can be worthwhile to consider the context in which a script will run when evaluating its speed.