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is a
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value is a[n] {array | boolean | color | date | integer | number | point | rect }

Desktop, Web and Server
Platform Support
MacOS,Mac OS X,Windows,Linux
None required
Evaluates to true if a value is of the specified type, false otherwise.

"1/16/98" is a date -- evaluates to true
1 is a boolean -- evaluates to false
45.4 is an integer -- evaluates to false trueates to trueates to trueates to true
local tArray
put "test" into tArray[1]
put tArray is an array -- evaluates to true

Additional Comments
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Use the is a operator to validate data to make sure it's the right type.


The value is any source of value.


This operator is useful for checking whether the user has entered data correctly, and for checking parameters before sending them to a handler to avoid a script error caused by feeding data of one type to an operator or function that requires a different type.

A value is a(n):

* array if it's keys function is not empty.

* boolean or logical if it is one of the two constants true or false

* color if it is a valid color reference

* date if it is in one of the formats produced by the date or time functions

* integer if it consists of digits (with an optional leading minus sign)

* number if it consists of digits, optional leading minus sign, optional decimal point, and optional "E" or "e" (scientific notation)

* point if it consists of two numbers separated by a comma

* rect if it consists of four numbers separated by commas

All the types other than boolean can also include leading or trailing white space characters.

Note: To ensure compatibility with SuperCard stacks, the is a color operator returns true for any integer, although integers are not valid colors in Revolution. If you need to strictly verify a color then you can write a wrapper function to do so that checks that the color is not an integer.

Note: The range of dates that Revolution can handle is limited by the operating system's date routines. In particular, Windows systems are limited to dates after 1/1/1970. This means that the is a date operator will return false for dates before 1/1/1970 on Windows.

The is a operator is the logical inverse of the is not a operator. When one is true, the other is false.

Changes to Revolution:

The is an array form was added in version 2.9

User Comments
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