Concept:
Type constraint
Headline
A means of constraining a polymorphic type
Illustration
The notion of type constraint is pretty general as it occurs in different ways in programming languages which is why we do not attempt a comprehensive description here. Instead, we briefly compare how type constraints show up in Java versus Haskell.
We use the following problem to illustrate type constraints: Suppose you want to count the elements in an array that are greater than a given element. This sort of function (or method) would need to be parametric in the element type of the array and that type would also need to be constrained to admit comparison.
Type constraints in Java
The type signature for a suitable method for the problem at hand is of the following form:
public static <T extends Comparable<T>> int countGreaterThan(T[] anArray, T elem)
Type constraints in Java
The type signature for a suitable function for the problem at hand is of the following form:
countGreaterThan :: Ord t => [t] -> t -> Ordering
Haskell's type constraints are discussed in more detail in the broader context of type signatures.
Marcel Heinz
edited this article at
Wed, 31 Jan 2018 12:18:32 +0100
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For you are available next options:will make text bold.
will make text italic.
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will allow you to paste code headline into the page.
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will allow you to paste code with syntax highlight into the page. You will need to define used programming language.
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