Difference between revisions of "Type"
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| − | You want to do this, for instance in order to define a whole new set of operators. | + | You want to do this, for instance in order to define a whole new set of [[Operator|operators]]. |
| − | Otherwise the operator definitions for the type it was cloned from would still apply. | + | Otherwise the [[Operator overloading|operator definitions]] for the type it was cloned from would still apply. |
== see also == | == see also == | ||
* [https://www.freepascal.org/docs-html/ref/refse19.html § “Type Aliases” in the Reference Guide] | * [https://www.freepascal.org/docs-html/ref/refse19.html § “Type Aliases” in the Reference Guide] | ||
Revision as of 14:18, 23 August 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 the type it was cloned from would still apply.
