Inside Macintosh: AppleScript Language Guide / Part 2 - AppleScript Language Reference

Chapter 3 - Values

Coercing Values

AppleScript coerces values in two ways:

• in response to the As operator
• automatically, when a value is of a different class than was expected for a particular command or operation

The As operator specifies a particular coercion. You can use the As operator to coerce a value to the correct class before using it as a command parameter or operand. For example,

set myString to 2 as string

coerces the integer 2 into the string "2" before storing it in the variable myString. Similarly,

"2" as integer + 8

coerces the string "2" to the integer 2, so that it can be added to the other
operand, 8.

If you provide a command parameter or operand of the wrong class, AppleScript automatically coerces the operand or parameter to the expected class, if possible. For example, when AppleScript executes this statement,

repeat ( word 2 of document "Big" of application ÿ   "Scriptable Text Editor") times
      display dialog "Hello"end repeat

it expects the number of times to be an integer. To coerce word 2 of document "Big" of application "Scriptable Text Editor" to
an integer, AppleScript gets the value of word 2 of document "Big"
of application "Scriptable Text Editor"--a string--and then coerces it to an integer, if possible.

Not all values can be coerced to all other classes of values. Figure 3-3 summarizes the coercions that AppleScript supports. To use the figure, find the class of the value to be coerced in the column at the left. Search across the table to the column labeled with the class to which you want to coerce the value. If there is a square at the intersection, then AppleScript supports the coercion.

Reference values are not included in the table because applications determine whether the value of an object specified by a reference value can be coerced to a desired class.

For more information about each coercion, see the corresponding value class definitions in this chapter.

Note

When coercing strings to values of class Integer, Number, or Real or vice versa, AppleScript uses the current settings in the Numbers control panel for decimal and thousands to determine what separators to use in the string.

When coercing strings to values of class date or vice versa, AppleScript uses the current settings in the Date & Time control panel for date and time format.

Figure 3-3 Coercions supported by AppleScript

Three of the identifiers mentioned at the top of Figure 3-3 act only as synonyms for other value classes: "number" is a synonym for either "integer" or "real," "text" is a synonym for "string," and "styled text" is a synonym for a string that contains style and font information. You can coerce values using these synonyms, but the class of the resulting value is always the appropriate value class, not the synonym. Here are some examples:

set x to 1.5 as number
class of x
--result: real

set x to 4 as number
class of x
--result: integer

set x to "Hello" as text
class of x
--result: string