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101

Compile-Time Results A-1

APPENDIX

The Inside Story on Declare A

This appendix describes the technical details of the declare mechanism. Knowing

these technical details is not necessary to understanding what declaring a view

means; they are provided primarily for completeness and to help you when you are

debugging. You shouldn’t write code that depends on these details.

For a basic discussion of the declare mechanism, see the section “View Instantiation”

beginning on page 3-26. You should be familiar with that material before reading

this appendix.

To serve as an example here, imagine a calculator application whose base view is

named “Calculator.” It has (among others) a child view named “Display.” The

Display view is declared in the Calculator view. See Figure A-1 for an illustration

of this example.

In the following sections, we’ll explain what happens at compile time and at run

time as a result of the declare operation. A number of slots are created, which

you may see in the Newton Toolkit (NTK) Inspector if you are examining the

view templates.

Compile-Time Results 26

As a result of the declare operation, at compile time, NTK creates a slot in the place

where the view is declared—that is, in the Calculator template. The name of the slot

is the name of the declared view,

Display. This slot’s value is initially set to nil.

Another slot, called

stepAllocateContext, is also created in the Calculator

template. This slot holds an array of values (two for each view declared there). The

ﬁrst value in each pair is a symbol used by the system at run time to identify the

name of the slot in the Calculator view that holds a reference to the declared view.

This symbol is simply the name of the declared view,

Display.

The second value in each pair is a reference to the template for the declared view.

At run time, the system will preallocate a view memory object for the declared

view from this template.

Figure 27-0

Table 27-0

1 2 ... 900 901 902 903 904 905 906 907 908 909 910 ... 941 942

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