Jus12 - 1 year ago 311
Scala Question

Scala forall example?

I tried Google search and could not find a decent

`forall`
example. What does it do? Why does it take a boolean function?

The `forall` method takes a function `p` that returns a Boolean. The semantics of `forall` says: return `true` if for every `x` in the collection, `p(x)` is true.

So:

``````List(1,2,3).forall(x => x < 3)
``````

means: `true` if 1, 2, and 3 are less than 3, `false` otherwise. In this case, it will evaluate to `false` since it is not the case all elements are less than 3: 3 is not less than 3.

There is a similar method `exists` that returns `true` if there is at least one element `x` in the collection such that `p(x)` is true.

So:

``````List(1,2,3).exists(x => x < 3)
``````

means: `true` if at least one of 1, 2, and 3 is less than 3, `false` otherwise. In this case, it will evaluate to `true` since it is the case some element is less than 3: e.g. 1 is less than 3.

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