Proposal: 'exists' in <algorithm>

[Marco Nef]

Reason

When someone just wants to check if an element exists in a container they have to write the following code:

if(std::find(begin(container), end(container), item) != end(container)) { ... }

There is always a duplication of end(container) which usually leads to very long lines and thus to less readable code than possible.

Solution

New function std::exists that returns a bool instead of an iterator:

template<class InputIt, class T>
InputIt exists(InputIt first, InputIt last, const T &value);

This function allows compacter Code, e.g. example under 'Reaseon':

if(std::exists(begin(container), end(container), item)) { ... }

The name exists can be exchanged by any other if there is a better naming. 

[Richard Hodges]

Isn’t this simply:

if (std::one_of(begin(c), end(c), [&model](auto&&x) { return x == model; }))

{

  ...

}

Perhaps this argues for a std::equal_to<X>(X&& model) factory function that generates the appropriate unary function.

?

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[Marco Nef]

Am Mittwoch, 14. Juni 2017 12:19:55 UTC+2 schrieb Richard Hodges:

Isn’t this simply:

if (std::one_of(begin(c), end(c), [&model](auto&&x) { return x == model; }))

{

  ...

}

std::one_of does not exist, but you're right: it's std::any, right? 

[Richard Hodges]

oops! You’re right.

I have however, often missed the presence of half-bound binary predicate

[Marco Nef]

oops! You’re right.

 

Not quite, it's std::any_of ;-)