Abstract type: Difference between revisions
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You can declare a virtual function to not have an implementation by using <code>F.virtual.abstract</code> keyword. A type containing at least one abstract virtual function cannot be instantiated.
<syntaxhighlight lang="11l">T AbstractQueue
F.virtual.abstract enqueue(Int item) ->
T PrintQueue(AbstractQueue)
F.virtual.assign enqueue(Int item) ->
print(item)</syntaxhighlight>
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===Interface===
{{trans|F#}}
<syntaxhighlight lang="cobol">
INTERFACE-ID. Shape.
PROCEDURE DIVISION.
IDENTIFICATION DIVISION.
METHOD-ID. perimeter.
DATA DIVISION.
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END METHOD perimeter.
IDENTIFICATION DIVISION.
METHOD-ID. shape-area.
DATA DIVISION.
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IDENTIFICATION DIVISION.
CLASS-ID. Rectangle.
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INTERFACE Shape.
IDENTIFICATION DIVISION.
OBJECT IMPLEMENTS Shape.
DATA DIVISION.
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PROCEDURE DIVISION.
IDENTIFICATION DIVISION.
METHOD-ID. perimeter.
DATA DIVISION.
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01 ret USAGE FLOAT-LONG.
PROCEDURE DIVISION RETURNING ret.
COMPUTE
GOBACK.
END METHOD perimeter.
IDENTIFICATION DIVISION.
METHOD-ID. shape-area.
DATA DIVISION.
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01 ret USAGE FLOAT-LONG.
PROCEDURE DIVISION RETURNING ret.
COMPUTE
GOBACK.
END METHOD shape-area.
END OBJECT.
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{{trans|Go}}
<syntaxhighlight lang="emal">
^|EMal
|but can use interfaces.
|^
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=={{header|Java}}==
Java has an
For an
A
A method with no access modifier is inherently
Member fields are allowed, although are effectively
Here is an example of an
<syntaxhighlight lang="java">
interface Example {
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}
</syntaxhighlight>
The
The
Additionally, if a method is marked
Here is an example of an
If the class contains <code>abstract</code> methods then the class definition must also have the <code>abstract</code> keyword.
<syntaxhighlight lang="java">
abstract class Example {
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}
</syntaxhighlight>
Here is an example of a class which
<syntaxhighlight lang="java">
public int methodC(int valueA, int valueB) {
return valueA + valueB;
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END TEXTHASHKEY;
</syntaxhighlight>
=={{header|Skew}}==
{{works with|skewc|0.9.19}}
In Skew, interfaces must be explicitly implemented with `::`.
<syntaxhighlight lang="skew">
@entry
def main {
var rgb = Rgb.new(0, 255, 255)
var hex = Hex.new("00ffff")
var color Color
color = hex
color.print
color = rgb
color.print
(hex as Color).print
}
interface Color {
def toString string
def print {
dynamic.console.log(self.toString)
}
}
class Rgb :: Color {
var r int, g int, b int
def toString string { return "rgb(\(r), \(g), \(b))" }
}
class Hex :: Color {
var code string
def toString string { return "#\(code)" }
}
</syntaxhighlight>
=={{header|Smalltalk}}==
A class is declared abtract by responding to the query <tt>isAbstract</tt> with true, and defining the required protocol for subclasses to raise an error notification. Optionally, instance creation can be blocked (but seldom done, as you will hit a subclassResponsibility anyway soon). Typically, the IDE provides menu functions to generate these definitions automatically (eg. "Insert Abstract Class" in the refactoring submenu of the class browser):
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The act of giving a signature to a module is called ascription. There are two type of ascription:
Transparent (written <tt>:</tt>) and opaque (written <tt>:></tt>). If a structure is ascribed transparently,
none of the types are abstract. If it is ascribed opaquely, all types are abstract by default, but can be specified
explicitly in the signature, in which case they are not abstract.
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Then say we have a structure ListQueue which implements queues as lists. If we write <tt>ListQueue :> QUEUE</tt>
then the queue type will be abstract, but if we write <tt>ListQueue : QUEUE</tt> or <tt>ListQueue : LIST_QUEUE</tt> it won't.
=={{header|Swift}}==
Swift uses Protocols to provide abstract type features. See [https://docs.swift.org/swift-book/documentation/the-swift-programming-language/protocols/ the docs]
A trivial example showing required properties and methods, and the means of providing a default implementation.
<syntaxhighlight lang="sml">
protocol Pet {
var name: String { get set }
var favouriteToy: String { get set }
func feed() -> Bool
func stroke() -> Void
}
extension Pet {
// Default implementation must be in an extension, not in the declaration above
func stroke() {
print("default purr")
}
}
struct Dog: Pet {
var name: String
var favouriteToy: String
// Required implementation
func feed() -> Bool {
print("more please")
return false
}
// If this were not implemented, the default from the extension above
// would be called.
func stroke() {
print("roll over")
}
}
</syntaxhighlight>
=={{header|Tcl}}==
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The Go example, when rewritten in Wren, looks like this.
<syntaxhighlight lang="
class Beast{
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