Apple Newton Utilities Guia do Utilizador descarregar pdf (Página 832)

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CHAPTER 23

Endpoint Interface

23-4 About the Endpoint Interface

If the input operation terminates normally—that is, the InputScript method is

called—the system automatically reposts the input spec for you to receive

additional input. Of course, you can alter this process if you want to.

Data Forms 23

All NewtonScript data needs to be transformed whenever it is sent to or received

from a foreign environment. That foreign environment may be a server or host

computer at the other end of the connection, or it may even be the communication

tool that’s processing the conﬁguration options you've passed to it. Typically,

communication tools expect C-type option data.

Whether you’re sending, receiving, or using data to set endpoint options, you can

tag the data with a data form. A data form is a symbol that describes the transfor-

mations that need to take place when data is exchanged with other environments.

When you send data or set endpoint options, the data form deﬁnes how to convert

the data from its NewtonScript format. When you receive data or get endpoint

options, the data form deﬁnes the type of data expected.

Data forms are used in output specs, input specs, and endpoint option frames. The

data form is deﬁned by a slot named

form in these frames. If you don't deﬁne the

data form in a particular case, a default data form is used, depending on the type of

operation and the type of data being handled.

Note that when sending data, you can take advantage of the default data forms by

not explicitly specifying a data form. Because NewtonScript objects have type

information embedded in their values, the system can select appropriate default

data forms for different kinds of data being sent. For example, if you send string

data and don’t specify the data form, the

'string data form is used by default.

The symbols you use to indicate data forms are

'char, 'number, 'string,

'bytes, 'binary, 'template, and 'frame. Each is best suited to certain data

and operations.:

■ For simple scalar values, use 'char for characters and 'number for integers.

■ For semi-aggregate forms of these kinds of data, use 'string for a

concatenation of characters plus a terminating byte, and use

'bytes for an

array of bytes.

■ For binary data, use 'binary. This is the fastest option for sending and

receiving, since the data processing is minimal.

■ For more complex data, there are two aggregate data forms. You may want to

use the

'template form if you're communicating with a remote procedure call

service that expects C-type data and that follows the exact same marshalling

restrictions the Newton does. The

'frame form is convenient if you're

exchanging frames with another Newton.

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