AppleScript: The Definitive Guide

Who Performs an Operation

Some operations within an interapplication communications context can be performed by the target application rather than AppleScript. There are two cases to consider. The operation may appear as a bare expression (for example, the condition in an if clause); I will call this a direct operation. Or, the operation may be part of a boolean test element specifier.

Direct Operations

According to Apple’s documentation, if the first operand of a direct operation is a reference to an object of the target application, the target application performs the operation. So, for example:

tell application "Finder"
        if the name of folder 1 contains "e" then

The comparison performed by the keyword contains is one of the operations that can be performed by the target application. The object the name of folder 1 is a Finder object, so in this case the Finder should perform the operation. In fact, though, experimentation shows that the Finder does not perform the operation; AppleScript does try to get it to do so, but the target application replies with an error indicating that it doesn’t wish to perform that sort of operation. AppleScript thereupon adopts a new strategy: it asks the target application for the values in question, and performs the operation itself.

So, the way AppleScript first tries to deal with the operation in the previous example is by sending the Finder a single Apple event that means: “Please tell me whether the name of your folder 1 contains "e“.” The Finder ...