Difference between revisions of "Type"
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== custom type definitions == | == custom type definitions == | ||
| − | <syntaxhighlight lang="pascal" enclose="none">type</syntaxhighlight> starts a section, where the programmer may associate identifiers with new data types, especially structured data types such as [[Record|records]]. | + | <syntaxhighlight lang="pascal" enclose="none">type</syntaxhighlight> starts a section, where the programmer may associate [[Identifier|identifiers]] with new data types, especially structured data types such as [[Record|records]]. |
<syntaxhighlight lang="pascal" line highlight="3"> | <syntaxhighlight lang="pascal" line highlight="3"> | ||
program typeDemo(input, output, stderr); | program typeDemo(input, output, stderr); | ||
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== type aliases == | == type aliases == | ||
In a <syntaxhighlight lang="pascal" enclose="none">type</syntaxhighlight> section aliases to already existing or previously defined data types can be declared. | In a <syntaxhighlight lang="pascal" enclose="none">type</syntaxhighlight> section aliases to already existing or previously defined data types can be declared. | ||
| − | The following example utilizes [[Conditional compilation|conditional compilation]] to alias the largest available unsigned integer type as <syntaxhighlight lang="pascal" enclose="none">wholeNumber</syntaxhighlight> (note there is already {{Doc|package=RTL|unit=system|identifier=nativeuint|text=<syntaxhighlight lang="pascal" enclose="none">system.nativeUInt</syntaxhighlight>}} defined). | + | The following example utilizes [[Conditional compilation|conditional compilation]] to alias the largest available unsigned [[Integer|integer]] type as <syntaxhighlight lang="pascal" enclose="none">wholeNumber</syntaxhighlight> (note there is already {{Doc|package=RTL|unit=system|identifier=nativeuint|text=<syntaxhighlight lang="pascal" enclose="none">system.nativeUInt</syntaxhighlight>}} defined). |
<syntaxhighlight lang="pascal" line highlight="3"> | <syntaxhighlight lang="pascal" line highlight="3"> | ||
program typeAliasDemo(input, output, stderr); | program typeAliasDemo(input, output, stderr); | ||
Revision as of 16:26, 25 January 2019
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The reserved word type is used to:
- start sections for user defined types, and
- identify a new type instance when referring to another data type.
custom type definitions
type starts a section, where the programmer may associate identifiers with new data types, especially structured data types such as records.
1program typeDemo(input, output, stderr);
2
3type
4 atom = record
5 electrons: longword;
6 neutrons: longword;
7 protons: longword;
8 end;
9
10var
11 x: atom;
12
13begin
14 x.protons := 1; // H
15 x.neutrons := 1; // D
16 x.electrons := 1; // 0
17end.
type aliases
In a type section aliases to already existing or previously defined data types can be declared.
The following example utilizes conditional compilation to alias the largest available unsigned integer type as wholeNumber (note there is already system.nativeUInt defined).
1program typeAliasDemo(input, output, stderr);
2
3type
4 wholeNumber =
5 {$ifdef CPU64}
6 qword
7 {$else}
8 {$ifdef CPU32}
9 longword
10 {$else}
11 {$fatal whole number too small}
12 {$endif}
13 {$endif}
14 ;
15
16begin
17end.
type clone
In a type section a type identifier preceded by the word type actually clones the type, with its type information, but creating different types.
1program typeCloneDemo(input, output, stderr);
2
3type
4 wholeNumber = type qword;
5
6begin
7 writeLn('qword: ', sysBackTraceStr(typeInfo(qword)));
8 writeLn('wholeNumber: ', sysBackTraceStr(typeInfo(wholeNumber)));
9end.
You want to do this, for instance in order to define a whole new set of operators. Otherwise the operator definitions for type it was cloned from would still apply.
