AppleScript: The Definitive Guide

Name

as — coercion

Syntax

                     value as class
                  

Description

When you use the as operator, you’re asking AppleScript to perform the coercion. If this is a coercion AppleScript is willing to perform (as described in the rest of this chapter), the result is a new value of the requested datatype. If not, there’s a runtime error.

Examples

9 as string -- "9"
9 as boolean -- error

Even though a variable’s value can be a class, you can’t use a variable as the second operand in a coercion. This won’t even compile:

set className to string
9 as className -- compile-time error

AppleScript must see a class name right there in the script at compile time, or it won’t parse the line. (I regard this as a bug.)

Do not confuse a coercion with an object string specifier! (See Section 10.9.) This is a coercion:

"xxx:" as alias

This is an object string specifier:

alias "xxx:"

The distinction can be crucial. There are circumstances where the coercion will compile but the object specifier will not. You can’t compile an alias specifier unless the file exists; but you can compile a coercion from a string to an alias, because the string is just a string. And there are circumstances where the object string specifier will compile but the coercion will not. You can form a file specifier using a pathname string, but you can’t coerce anything, not even a pathname string, to a file object.

A special case of coercion arises when you say as in the context of a get, implicit or explicit, targeted at an application. When you do this, ...