eiffel-org/documentation/21.11/_others/draft/multiple-inheritance.wiki

[[Property:title|Multiple inheritance]]
[[Property:weight|0]]
[[Property:uuid|7f54afce-fd1d-fba7-7a55-f74604ea9846]]
<h2>Multiple inheritance: definition</h2>

Multiple inheritance is a mechanism for combining abstractions. It lets you define a class by extending or specializing two or more classes, not just one as in <em>single</em> inheritance. For example you might define a multi_function printer as the combination of a printer and a scanner.

Multiple inheritance sometimes has the reputation of being complicated or even messy, but there is no such problem in Eiffel. "Name clashes", for example, are not a big deal: if classes <eiffel>A</eiffel> and <e>B</e> both have a feature with the same name <e>f</e> and class <e>C</e> inherits from both, you can either specify that they should be merged, or keep them separate through the <e>rename</e> mechanism. Details below.

 <h2>Multiple inheritance basics</h2>

Multiple inheritance happens as soon as you list more than one class in the <e>inherit</e> clause at the beginning of a class. For example:

<eiffel>
	class PRINTER feature
		... Here the features specific to printers ... 
	end

	class SCANNER feature
		... Here the features specific to scanners ...
	end

	class MULTI_FUNCTION_PRINTER inherit
		PRINTER
		SCANNER
	feature
		... Here the features specific to printer-scanners ...
	end
</eiffel>

As with single inheritance, the new class has access to the parent features, except that here they are features of two different parents. For example if <e>PRINTER</e> has feature <print>  and <e>SCANNER</e> has features <e>scan</e> and <e>scanned</e>, then the feature clause of <e>SCANNER</e> can include

<code>
	scan_and_print
			-- Scan a page and print it.
		do
			scan				-- Leaves result of scan in `scanned'
			print (scanned)
		end
</code>