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Programming-Idioms

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  • Perl

Idiom #288 Check if set contains a value

Set the boolean b to true if the set x contains the element e, false otherwise.

$b = $x{$e};

Here we are using hash variable %x as a set and assuming that when keys are inserted the corresponding value will be set to a true value; i.e. anything other than undefined or zero.

If the values could be undefined, then it would be necessary to make the expression 'exists $x{$x}'.

Alternatively, use Set::Scalar for real set operations.
b = x.find(e) != x.end();
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$b = $x{$e};

b = x.find(e) != x.end();
b = x.Contains(e);
var b = x.contains(e);
b = x(e)
_, b := x[e]
b := x[e]
b = e `member` x
let b = x.has(e);
boolean b = x.contains(e);
(setf b (not (null (member e x))))
b := e in x;
b = e in x
b = x.include? e
let b = x.contains(&e);